The beginning of Episode One is essentially a long, interactive cutscene. Players of Half-Life 2 will recall the fact that you won your battle with Dr. Breenís forces atop the Combine Citadel in the heart of City 17, but at a grave price; your struggle caused a massive explosion, destroying much of the citadel and seemingly vaporizing Alyx, your companion. As you discover at the beginning of Episode One, however, the Vortigaunts were capable of both saving Alyx and preventing the G-Man from enlisting you back into his services as he wished to do. From there, both you and Alyx are somehow deposited at the base of the Citadel, ready to take up the fight against the Combine once more.
Thatís where your journey begins, and as we mentioned, youíre just going to be along for the ride for a while. After Dog moves the Combine assault ship out of your way, drop down to the ledge and crawl around to the nearby platform, using your gravity gun to blast the car out of your way. A short while later, Dog will throw you and Alyx across the gap into the Citadel, leading to a little roller-coaster ride that you probably shouldnít be able to survive. But survive you do, as has been a theme in the life of Gordon Freeman. Itís time to find the Citadelís power core and find a way to contain the imminent explosion thatís about to occur.
Onwards And Inwards
When you get past the first loading screen here, hop off the platform that youíre on and reach the platform below you. Before long, youíll come to a dead end: a pair of stalkers are holding up a force field in your path which Alyx canít break through. Youíll have to kill the stalkers to get through the field, but thatís going to be easier said than done.
As Alyx notes, though, there are rollermines being shunted through a set of nearby tubes. If you could manage to grab one of them, then you might be able to use them for your own nefarious purposes. After she shuts down the smaller forcefield here, crouch through the small passage here and crawl around until you can start dropping down to the platforms below you. When you hit the level of the elevator, pass over it and hit the switch beneath the clogged tube of rollermines. Theyíll all issue forth at once, so zap them with your gravity gun until most of them fall away, then grab one and ride the elevator back up to Alyx. Sheíll zap it to change its targeting parameters, allowing you to chuck it through the forcefield and kill the stalkers. Just keep in mind that itíll eventually turn red and explode, so do your best to keep it away from you when it does so.
The path from here is long but linear. When you spot the dead soldiers, blast the debris out of your path with your grav gun, then run on. Youíll eventually have to jump over a small balcony to move on, and youíll soon come to a energy platform with more soldiers on it. Worry not, though, as theyíll get sucked into an energy vortex off to your right. The only problem is how to get past the vortex yourself...
Well, thatís where your sprint key comes in. Itís pretty basic platforming; just wait for the vortex to wind down, then sprint across the platform before it starts up again.
The next room will finally see you come face to face with one of what we suspect to be the master race in the Combine forces. This massive, slug-like alien entity (or one like it) was last seen negotiating with Breen as he attempted to escape from the Citadel, and apparently hasnít managed to effect its own exit from the collapsing structure just yet. You canít interact with it, and as soon as you spot it, it appears to initiate its own teleportation out of town. Surely weíll be seeing more of them in the future, however.
The Mischievous Platforms
After getting your gravity gun supercharged, youíll finally be able to defend yourself against the soldiers of the combine, and as such, you can expect to start seeing more of them. As a reminder, you can either hit your primary attack to blast them away from you at short range, or use your secondary attack to grab them and start dragging them towards you. Either attack automatically kills your foe.
When you reach the platform that appears to extend an energy walkway, you have to figure out how to activate the walkway. Doing so is pretty simple: just grab one of the white energy balls that are floating around above you with the gravgunís secondary attack, then blast it towards one of the two receptacles below you. If you hit it correctly, you should spot the receptacle sucking in the energy ball and using it to power up one half of the platform. Nail both of the receptacle, and youíll be able to pass along.
Now, as you move across to the middle section of the area, youíll be forced to do all this again, but this time youíll have soldiers fighting against you. Alyx will do her best to keep them off your back, but youíd be well advised to clear out a few of them with your gravity gun before attempting to enable the next platform in front of you. (Donít forget that Alyx can die on Hard mode, so be sure to protect her if youíre playing on the highest difficulty.)
Itís the third platform that will be most difficult to activate, due to the fact that one of the two receptacles here is blocked off by a piece of fallen debris. After powering the non-blocked receptacle, move around to the left and find the small passage that allows you to walk over and on top of the second receptacle. In order to power it, you have to nab an energy ball and shoot it downwards so that it banks off the debris and back into the receptacle. Donít worry, itís not as difficult as it sounds; just be sure to clear the area of soldiers before attempting to do it.
After some more misadventures in the Citadel, you and Alyx will reach a massive central elevator thatíll take you down further, further towards the core. In order to activate it, get ready to throw some more balls towards the receptacles in the elevator shaft, and be ready to grab falling debris from above. If you can suck it in with your gravity gun, you can toss it into one of the white strings of energy to disintegrate it.
When the elevator stops for the first time, remove the computer console from the nearby platform and then bank an energy ball through the hole thatís thusly created; after a couple of tries, you should be able to get it into the receptacle behind the window and resume your descent. At the next stop, the banking is fairly easy to perform, but a stalker will appear and zap your energy ball before you can resume the descent. To prevent it from doing so, bank an energy ball towards the stalker to kill it, then bank another one towards the receptacle. Just be ready to run when your elevator hits the bottom floor....