Uncertainty Principle

for Half-Life 2: Episode Two

When the Combine raid your Resistance hideout, you are forced to flee into the depths of the Outlands.

But with Overwatch forces hunting you down, and the local fauna out to get you, danger is always just around the corner.

Play through four chapters of Half-Life gameplay, exploring new locations, meeting new characters and uncovering lost secrets.

Basic Details
  • Title: Uncertainty Principle
  • Filename: hl2-ep2-sp-uncertainty-principle.7z
  • Size : 83.40MB
  • Author: Alastair Toft AKA MisterAddy
  • Date Released: 26 September 2015

Download Options

Download to your HDD [83.40MB]
You can still use it with MapTap once you have downloaded it.

Manual Installation Instructions
  • Copy the uncertaintyprinciple folder into your …\Steam\SteamApps\sourcemods\ folder.
  • Restart or start Steam.
  • Half-Life 2: Uncertainty Principle should now be listed in your Library tab.

If you require more help, please visit the Technical Help page.

Download The Source Files

Alastair has kindly decided to allow the source files for this mod to be made available. There is a readme file in the archive, please read it. If you don’t know what these files are, they are for modders to have access to the original files – players DO NOT NEED these files.

Download to your HDD [4.70MB]



WARNING: The screenshots contain spoilers.
Screenshots to follow.

Reader Recommendations
Avoid It!
Think Twice
Play It Later
Play It Now!

13 recommendations, average score: 4.77 (out of 5), standard deviation: 0.18 (what's that?)
Total Downloads
  • 3,327
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    Last 7 days
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    Last 30 days
  • 1,459
    365 days
Meta Review Data
Statistics based on 14 comment(s) with meta review data.

Using Gauge: 0 Users
Manually: 14 Users

Time Taken:
Average: 3 Hours, 48 Mins
Shortest: 2 Hours by Bastion
Longest: 6 Hours by
Total Time Played: 53 Hours, 7 Mins
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  1. OJJ

    Well I have mixed feelings about this mod, on one hand it is one of the best looking long mods that have come out but on the other, the combat is really overbearing. (I was playing on hard so you’ll probably have a better time on other difficulties.)

    Parts like the intro or the boat chase are really well done and really quite thrilling. But there are quite a few times when the mod gets ridiculous like the part where you have to fight a hoard of Antlions, a guardian and avoid a gunship at the same time, or the final map which ends with a battle that goes on for so long with such little rest that the game plays three 2+ minute music tracks and then some before the end.

    The checkpoints are really scarce, the possible worst offender being the part where you have to replay a slow moving raft ride after dying two minutes after it ended and some are a little questionable like re-spawning you outside of a crank door that you most likely already opened before you died and you now have hold E for another 20 seconds before you can progress to where you died. Thankfully F6 works in this mod so you can use your own checkpoints instead.

    Overall it was a very enjoyable experience with some moments that I won’t talk about so anyone reading this can play through and find out on their own.

  2. Play It Later

    My goodness… Its hard to really explain this one, I like it, and I kinda hate it with the strength of a thousand burning suns.

    Really when it comes down to it, the mod does not do anything /bad/ as in, its not got overwhelming glitches or massive design flaws in the levels. But for me I got plenty of smaller glitches and problems throughout the entire mod, which nearly had my throw my keyboard out of the window. Lets go into detail.

    -STORY- No spoilers 🙂
    It is really your basic story, Combine attacks the resistance and you must head out by yourself for the most part, however you do get a companion for about ten minutes and then never again. You have to do multiple tasks, first you have to escape from your old base; setup a radio tower and then escape the area.

    Now the issue is that really the game only had a story for the first half, after that things are very silent and I kinda wish the mod found a way to end things there, it would have made things more tight and cohesive overall in regards to the storyline, or at least expand it and provide context to the rest of the levels.

    I will say though it was quite cool at the end, I won’t spoil things but it was a nice surprise.

    It was quite good, you wake up and are getting raided by combine, so you have to make your way out of the place alive while many rebels around you die, during this you meet the guy who will cover your ass for the rest of time, shortly after you get your hands on a jeep and you drive as far as you can, some well placed music plays and you drive out, dodging gunfire, strider attacks and the like.
    However my dislikes are more nitpicks than anything to be honest, for example guns from dead rebels did not drop, and the combine placement meant I had to run into hugging distance to get past them which caught me off a few times. On top of that the driving at the end, while great was not very well designed in terms of direction at some parts. Turns being too sudden after another turn for example, I crashed and got stuck a couple of times as well and died trying to free myself.

    -Main levels-
    They are good, got a decent Half Life feeling from them as I played and it did manage to mix a fair share of physics puzzles alongside combat quite well. Which I feel like not many mods do these days.
    Getting the radio tower back up was very well designed as well, binding all three locations together with a small ‘arena hub’ as I would call it. You will cross through this section during each of the three tasks and once you complete them the hub changes in some way, normally with a fight.
    Going up to handle the radio tower was not a big problem to me, even with the attacks from the combine frequently.
    The tower was the highlight for me, after that I was expecting things to close out but it never did. Not for another hour at least.

    What was wrong with the levels? Well, I had a frequent problem
    I remember Jim Partridge always telling map makers that
    “The player must be alerted that they will be placed into a environment where they will take damage, and if you do not then you are cheating the player by not giving them the ability to avoid the damage”
    Unfortunately I feel the mod maker overlooked this greatly as I was ambushed constantly without warning, this did not even apply to the main path, I was walking to some crates when the floor gave in and brought me face to face with 7 headcrabs, all of which lounged at me before I realised what just happened. The game throws this at you all of the time and to be honest it really starts to make me angry when it keeps happening especially when the ambushes killed me without giving me the chance to avoid such.

    The later levels in the mid and final chapter were frustrating as well, I remember specifically one thing. god damn, Strider fight.
    If there is one thing I wish was cut from HL2, it was these darn things. They’ve never been fun to me and never will, so when I was placed into a arena against one as well as multiple combine soldiers, I died a lot.. Way too many times. Nearly dropped the mod entirely after that.

    Pacing is a bit of a problem for this mod as well, after dealing with a massive arena fight I got hit with more enemies to fight straight after. There was never really any point in the game I can remember that gave me a moment to properly relax after a big fight. The mod was just combat throughout and it left me fatigued of fighting as I neared the end.

    It was just like the rest of the mod, closed out with a arena fight that was a bit longer than I feel like it should have, although credit to the map maker as it did give a slightly more quiet beach part against antlions (Although I could hold space on the water and dodge the leaches and sand entirely)
    On the plus side, our friend shows up with some nice toys. so it was a bit of a surprise.

    With a mod this size, there were bugs, not many though

    First was after the antlion attack at the elevator, the NPC walked in and hit the switch, then got stuck in the door and broke the game. Had to redo the arena fight as it autosaved after he got stuck.

    Some prop clipping issues here and there. But that summed up the bugs for me.

    -Things that made NO sense-
    First off, I cleared out a house and suddenly a combine sniper appeared in there as I walked out

    The ending pickup I don’t understand. Mainly because one, how did our friend find the player. But second, why could he not just get us after the radio tower was handled.

    There were a few others things although the length of the mod leaves me struggling to remember things.

    It is good, but I wish it just ended after the radio tower was done, after that I feel things are dragged out too long and really lose focus, the first half is GREAT. but the second half will leave you fatigued and sort of sours the experience for me at least

  3. Play It Later

    My reaction to this mod is very love-and-hate. There’s no doubt that it has its moments. Powering up the radio tower, for example, was a neat structural throwback to Blast Pit. The airboat ride is a reasonably good take on the Water Hazard concept. There’s even a nifty segment where you’re being carried along by rushing water. The forest highlands are also a memorable setpiece with nice lighting, as they were in the original BeginningVille iteration of the level.

    But there are other things the mod does which just make me rage. The non-stop onslaught of enemies that give you no room to breathe being the main offender, but also things like repopulating areas with enemies behind your back, uneven placement of health pickups, brutal checkpoint placement, even magically placing Combine locks on doors you could previously go through.

    It’s really the combat the drags this mod down. I can’t count the number of times I muttered “This is ridiculous” to myself. It makes this long mod feel long because it simply has too few ideas to sustain its lengthy run time. For the most part, it’s like you’re fighting the same battle over and over again with Combine that come barreling around the corner with guns blazing. Damage rarely feels avoidable because you only have a split-second to react, cover is often absent, and those Antlion Workers… well, the less said about their obnoxious placement the better. And like I said before, health pickups were really sporadic as well, with suit energy hard to come by throughout most of the mod. I felt supply crates seldom gave me what I needed most.

    I also encountered a serious bug early on at the end of the first level where 4/5 times I was stuck on a white screen and the next level failed to load.

    I hate to be so down on this mod because it’s clear a ton of work went into it. But I just didn’t have much fun with it. Sorry. It’s not a bad mod, but I’d rather see the author polish the handful of memorable setpieces and take a hacksaw to everything in between.

  4. Play It Now!

    I quite liked this mod. There was a lot of good content, and the difficulty level on easy was just where I like it. Some of these maps I have played before (I believe from PP contests?) but I thought everything was joined together nicely. The best part was where you are in the rushing water.

    The ending was a bit too much repetitive combat, but for such a long mod I can forgive that. I also thought that maybe there was spawning of combine in one space, so after killing about a dozen of them I gave up and moved on. The rebel did get stuck with his foot in the elevator gate the first time and so the elevator didn’t move. Reloading and making sure I moved to the very back solved the problem. I also thought the bridge part was kind of unfair. It’s hard to know the solution until you have played it the first time.

    Overall it wasn’t perfect but it was definitely a PIN for me. I will be playing this one again.

  5. OJJ

    Oh, on a sidenote I don’t think the banner image does the visuals of the mod justice, might turn a few people who haven’t seen other pictures of this mod away from playing it.

    1. I’d agree with that. I know more screenshots are on the way, but I don’t think we can overemphasize how large this mod actually is. It’s easily 2 hours long and, at times, much more photogenic than that one screenshot. X)

      1. Yes, you are both right, sorry. I’ll change it immediately after I get back in a couple of hours.

  6. I think it looks and plays great! Nice mix of challenges but the combat was a little unbalanced

    1. I have removed the recommendation image from this review. Two short sentences for over 2 and a half hours is not enough to allow the image. I have also edited the “99 hours” to 2.5. Please let me know if you have the correct time.

  7. Play It Later

    First off gratz on the huge amount of work here. I know how hard it is to finish a mod of this length. Takes serious commitment and you can hate it by the end. Well done getting it over the line..

    There’s fun to be had in this mod and the mapping quality is OK (a bit blocky in places and not enough verticality for my liking…
    The mod starts out really well and then gets rather sloppy from the radio tower section onwards.
    This mod could REALLY use some story sequences to break up the puzzles and action. Not sure why this mod suffers more than most but I got bored pretty quickly.

    Mapping can be rather flat and grey. Way too much concrete texturing for my liking…

    It’s also brutally hard.. needs way more health kits dispersed through the mod. As the player has the grav gun there’s no reason not to scatter them around..

    Overall nice ideas done well a lot of the time… just way too long and samey for my liking. Combat fatigue is certainly an issue…
    Nice to see the airboat being used in conjunction with hunters.. that’s a new one..

    1. Going to add a few more comments as I feel there’s so much to talk about but it’ll occur to me along the way:

      Voice Acting – Really Good!!! Interesting voices and didn’t sound like just some guy.
      Lip Synching – huge props to anyone who gets this to work. i’ve struggled for so long and still can’t get this working. its very fiddly… perhaps a tutorial on this site would be really appreciated!

      1. I have a tutorial on my site that explains how to set up Faceposer for lip syncing. I personally don’t attempt to adjust the phonemes beyond the automated result because the program is so crashy. I’ve dealt with worse, but Faceposer never stops being “fiddly.” Once a line processes correctly, you don’t want to touch it ever again. Since you feed it the text it’s supposed to listen for, sometimes you have to cheat and spell words phonetically so it can understand it. Depends a lot on the voice actor. Faceposer stumbles on some more than others, especially if you have a lot of hemming and hawing. There’s often a need to break up a line into smaller chunks, as shown by many of G-Man’s lines. Unless you’re Rob Martens, in which case you could read the whole dictionary and somehow it will process without trouble. X)

      2. whats the best site to teach you the hammer editor in easy to understand guides .. i have a basic knowledge of the hammer editor and can understand how to make rooms,use triggers and placing sounds and npc,s but i want to know more .. cant find a site thats suitable .. thanks jim !

        1. Tophatwaffle does video tutorials for hammer on youtube. They’re excellent!

  8. Play It Now!

    I’m guessing 4 hours, though I suspect it was longer than that, I wish Steam would count hours played on mods.

    I really quite liked this mod, but it was definitely not a PF for a couple of reasons.

    It was long, and that was both good and bad. The good on that is, that the length offered me time to play around in different environments most of which were very pretty indeed. It had a story which did sort of stray a bit, but was pretty sound. The bad, though, was that it was often somewhat directionless and the pacing was off by a lot. It didn’t feel like a slog, but it wasn’t well-paced enough.

    The fighting was *positively brutal*, and I only played on Medium so I can only imagine what it was like for those who did it on hard. Good lord! Particularly any fight with antlions in it – what was up with them? They felt indestructible!

    On the other hand, I didn’t have much trouble with any of the Hunter fights, and the Guardian fight, while it did make me curse frequently, i thought with a little polishing could have been a magnificent fight area. There was good use of the scenery in that particular fight – but as someone else points out above, often enough what seems to have been a completely cleared out area, suddenly repopulates and that’s a very poor thing.

    The soundscapes were very nice, the parts where the shelling is going on above and you’re below in the water ways, in particular, that gave a sense of doom. You know there’s going to be a buttload of headcrabs out there when you emerge.

    The waterways! I almost wish that parts of this mod were released for Waterville, because they probably would have taken a PF from me for some of them. Visually, the waterfalls and the use of certain effects were really well done. The unfortunate side bar to that though, is that the ‘rancid/radioactive’ water has such a small texture that it quilts and repeats, so the wider areas which sported that feature were ugly indeed.

    I did have to use noclip once- I couldn’t get past the cliff side jumps. I have no idea how you’d manage to get from one of those pillars or the main trail to the next part, but … yeah I couldn’t, so I had to cheat a few yards. That was my only cheat though, even though I was quite tempted during some of those fights to put on Godmode and be done with it. I’m glad that I kept on it though, because every fight did come out feeling pretty thrilling.

    And That One Jeff! I didn’t know you were doing voices 😀 now I can say I knew you when, right?

    My one wish for this mod, which would probably have not made it any easier to fight or any quicker for pacing but would still have made me love it all the more, would have been the many, MANY times that Gman should have been in it. While I found a bunch of the ‘in the rain’ graffiti bits, there were plenty of locations where he simply should have been there – straightened his tie, and walked away. That’s kind of a touch that I do honestly wish the makers would go back and insert, because I would be over the moon with that, and I think it would have added a lot to the slower parts and given a bit of direction when we were in need.

    Definitely a Play It Now, though, because this is one great mod.

    1. I wish Steam would count hours played on mods.

      MapTap does – kinda.

  9. Zekiran

    (( Phillip, my comments keep getting eaten 🙁 ))

    1. Visible now, sorry about this. The system must not like you.

  10. Personal Favourite

    allthough theres been some mixed reviews about “uncertainty-principle” ive been extremely impressed with the mod,so much so ive given it a “personal favourite”
    granted there may be some minor issues with the mod but this does not change my mind .. this is a mammoth mod and the best ive seen this year ( by far )
    i cant imagine how long it took alistar to create this mod …. many mods made by one person can take between 2 and 3 years .. this takes so much dedication and time is also a problem when making mods … personally being married theres more to do on a daily basis than mapping/modding so theres no way i could create a mod as there is simply not enough time in the day to dedicate myself to a mod
    i wont go on about the mod itself … its stunning,well made and fun to play …. and theres no doubt alistar has a future in game development/creation …..
    excellent mod .. very happy .. well done alistar !

  11. grabbie

    I just played the first part of the mod and got a serious case of déjà vu. I know this part has been released sometime in the past. After looking it up, it was released in BeginningVille. Looking forward to playing the rest once I have more time.

  12. I think its fantastic people are still making long SP maps.
    and yes, some of the bits were, um, difficult.

    as I’ve said before, the best recommendation of a game is how quickly you replay it.

    Game On.

    1. My feelings exactly. The “desert” of lack of numbers of add ons is like being thirsty with little water in sight……

      I’m at the last map (I think) with nobody left to fight and a big ship hovering, but no ending per se. I suppose that’s it.

      1. If you just got into a fight with people by a lighthouse, this should help.

        Spent a while to work it out, when the helicopter lands, you are meant to press E on it. Instead of just being within a trigger.

        1. Thanks, that’s where I am, and after the extended battle with nobody left to fight, there is a dropship hovering well out of jumping or touching reach. I replayed from autosave, same thing. No helicopter appeared. Oh well, I suppose something messed up in the triggers and if I’m nearly at the end, it doesn’t matter.

          1. Yes, you are at the end. Perhaps the Dropship glitched. They can be very fickle things. I think I recall seeing it hovering in place for a while before something triggered. You may want to ensure you’ve killed every last Combine.

  13. Milliman4

    I didn’t play it, but it looks cool and I want to play it, but it downloads only one file, not the whole folder. Can someone help me?

    1. Okay, I am going to have to ask lots of questions.

      1. What program are you using to open the .7z file? I suggest 7zip.org
      2. Are you dragging the folder within the zip file across to the correct location?

      Have you visited this page: http://www.runthinkshootlive.com/th/ for more detailed instructions?

      1. I just drag the .7z files onto Maptap. More reliable than dropping unzipped files into the source mods folder.

  14. Heinz

    One of the best HL2-Mods I have ever played. Thats all to say!

  15. William

    I wanted to bring the gnome with me all the way… got all the way to the final chapter and the barnacle stole it from me when you’re rushing through the fast sewers… Poor mr. gnome.

    1. Oh, dear, eaten by a barnacle insight of freedom. What bad luck.

    2. Zekiran

      Are you talking about the hidden scary gnome, or was there one that you could grab easily? The only one I saw (that I remember anyway) was hiding halfway behind a shipping container that you couldn’t move in that Guardian fight venue. The creepy screenshot is in my steam gallery 😀

  16. Alastair has kindly decided to allow the source files for this mod to be made available.

    There is a readme file in the archive, please read it.

    If you don’t know what these files are, they are for modders to have access to the original files – players DO NOT NEED these files.

    The link is in the main post.

  17. GEORGE026


  18. Hec
    Personal Favourite

    I was battling inside my mind between recommend this one as a PN or a PF. And after a while I’ve decided to surely recommend this mod as a PF. Why? Well, just because the scarce mods we have nowadays this mod is really well done, with a clear neat exciting story. And it has just a lot of action and good quality maps to be a perfect PF.

    Something I liked in particular about this mod are those minor details that make me recognize them as some “old school” elements you know. Like those sometimes confusing paths where you have to cramp some boxes to climb some walls and go on. And stuff like that.

    I also enjoyed the airboat ride, It was just amazingly well done, and the battle against the Strider in that Dam was just great, possibly is the best use of the armored airboat I’ve seen in many, many mods I’ve played.

    I also loved the fact that this mod has plenty of combat and action it almost never lets you to get bored. From the beginning till the end is cool after cool battle, also the ending felt quite like a regular “escape the place” L4D2 SP campaign, but it was ok for me in this HL2 environment. }

    Overall I guess I just enjoyed this mod too much! got me entertained the 100 percent of the time and the maps in there were clever and just great, you know the part where you get to the antenna, the Strider part, and the last battle are just too memorable in this mod.

    I think for sure this mod has to be one of the best of 2015 here in RTSL.

  19. Personal Favourite

    One of my all time favourites, didn’t want it to end. The time taken is not accurate as I kept coming back to it over a number of weeks.
    The scenery and the sense of space is wonderful, I really enjoy the exploration and this had just the right amount of action and puzzles.
    I must confess to using ‘noclip’ at the rock jump and ‘godmode’ at the final battle, lifes too short and Im not that good, but these maps are few and far between and I will definitely enjoy playing this again. My favourite this year.
    Great job MisterAddy what a star.
    Oh, just an aside, I scanned through the other comments and didn’t see any other mention of credits – Voice Acting – Philip Marlowe ?

  20. Personal Favourite

    Great piece of Work! Awesome design and atmosphere. I really enjoy most of the mod and gameplay is very nice, but last fight in this mod is a bit too hard for many players – maybe not for me, but i think many people have had problems there, exactly on ”Hard” Difficult. There are some nice puzzles too, not too hard but well build and enjoyable.

    One of the best Half Life 2 Episode Two mods in 2015 . Very nice, I enjoy it a lot!

  21. Teh Engineer

    I enjoyed the mod, but I brought that freakin’ gnome all the way to the end and I wasnt sure what to do with it. Blarg.

  22. Personal Favourite

    Absolutely BRILLIANT!!!!

    This is now one of my fave mods out there. It’s not stupidly hard and is also really well balanced and the pace is just perfect. I loved the exploration. Fun and one I’m keeping installed. In fact, I’ll play it again. Suuuuuuperb!!!


  23. asterixer

    under Linux the elevator in the second part of the mod doesnt work. You can get into the lift and your friend is pressing the button, but nothing happens…

  24. Personal Favourite

    I can`t say much words about this mod. Its so amazing. I was expecting somekind of travel through forest and conclusion was Combine Base, as in corridor mod. But I found AWESOME locations, atmosphere, soundtracks.
    Perfectly balanced Action, Puzzle and Scene areas. There no need to run, you can stop and watch how beautiful the map is. Oh, I love this. How can I describe this mod? – Masterpiece.
    All four chapters were well-made, and must be rated as “Perfect”. Exept one thing: last fight in chapter 4, I mean it wasn`t unusual, just groups of enemies were running to me +playing at Hard gave me a lot of saves, because I was made to save after killing each NPC. Well, I truly thing that Finale will be fixed.

  25. For some reason it doesnt appear in my library when downloaded manually

    1. Are you copying the contents of the archive or the archive itself? Have you tried the Technical Help page.

      1. OJJ

        A bot outside of Zombie Fortified?

  26. Play It Now!

    Really phenomenal mod! Solid level design in combat areas feels very much like official Half Life content. Rewards exploring and taking your time (don’t break all the boxes!) Lots of detail in the environments and makes for some good wallpaper screenshots. Maps are very large and take a while to load on an HDD, but it’s worth it for the long periods of uninterrupted gameplay.

    Only complaint is that the loading screens and some parts of the last map render as wireframes for some reason.

  27. Personal Favourite

    Besides Transmissions E120, this is the best 2015 Source release, in classic HL2 style.

    The map’s are so beautiful and well-thought, you could just stare for minutes in some panoramic views, also there is that great and dynamic beginning like an AAA action blockbuster, great battle against a Strider… with an Airboat, it’s so rare to see someone use greatly an Airboat in a mod!!!
    However, after 3 greats maps/chapters, the last one is maybe a little “too much”, too dark, too hard, and with no great purpose… the beginning has too much antlions and I just ran away, then the final battle is not that great and too generic, after all the player has been through…

    Well, anways, your mapping skills were great and it felt like a good action movie.

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