The writer for Half Life posted the plot to Half Life Episode 3 on his blog.
http://www.marclaidlaw.com/epistle-3/
The site is getting hammered currently and the names have been changed to avoid copyright but yeah, this was Episode 3.
Here's a tl:dr of the post with the proper names:
-Gordon and Alyx head to Antartica and find a Combine base built around the Borealis, their helicopter gets shot down
-The Borealis is a weird shifting place that exists into two places simultaneously
-Breen as a Combine grub doesn't quite realize what happened to him, but hates his current state and after capturing Gordon and Alyx, asks them to kill him. Alyx refuses, but the player/Gordon can apparently do something to kill him
-Mossman claims that Eli had tasked her with being a triple agent for the Resistance all along
-They realize the Borealis is "stretched" between the past and present, not just two places in space; the Aperture scientists activated the device during the Seven Hours' War while the Combine was approaching and attempted to warp to Antarctica to be as remote as possible, but ended up warping into the future
-Time and space warp more around the Borealis and they get a glimpse of the Combine's headquarters they launch invasions from
-Mossman wants to "anchor" the Borealis in the present in Antarctica to safeguard it for the Resistance, Alyx wants to honor Eli's wishes and destroy it so it can never be misused; there's talk of the potential time paradoxes
-Mossman and Alyx fight, Alyx shoots Mossman
-Gordon and Alyx rig the Borealis to self destruct and create a missile that can travel between dimensions, essentially turning the Borealis into a time/space warping bomb aimed at the Combine base
-As they fire it, the G-Man suddenly appears and reveals that he's been keeping tabs on Alyx as some kind of sleeper agent (as hinted at in Episode 2) since the events of Black Mesa, and actually appears to Alyx (she remembers him) and takes her with him through his glowy train door as a "replacement" for Gordon, who he leaves to die
-The player sees that the Combine base is actually a massive Dyson sphere and there's no way the Borealis bomb will actually do any significant damage
-The Vortigaunts intervene and pull Gordon out right before the Borealis self destructs
And there you have it brehs, closure, bittersweet closure.
#fukkValve