Grab the pistol ammo from the supply crate, and head out on to the street. It would be wise to quicksave before you attempt the next section, as the snipers covering the road will take you down very quickly. Your sprint key will come in handy as you need to dash from cover to cover to advance up the street. Keep an eye on the blue lasers, as they'll tell you where the snipers are aiming. Once you reach the truck, shoot out the hotel window and race inside.

Listen to the resistance fighter tell you where Barney is, and grab the pistol ammo and suit battery from the supply crate. Sprint up the road and through the blue doors at the end on the left. Cue spooky music and headcrabs as you enter the warehouse. Just before you pass the bathroom on the left, a fast zombie will charge up the ramp ahead. Give him two barrels with the shotgun and grab the health in the bathroom before heading down the ramp to the flooded basement.

Follow the shouts for help in to a small room with a wounded resistance member. You'll find shotgun shells, health, and suit batteries in the supply crates next to him. Blast or crowbar the horde of zombies that emerge from the water, and then move through the basement towards the stairs. Two fast zombies will charge through the door ahead. Head up the stairs as far as they go, then rub your hands with glee as a Combine sniper pops the zombies coming towards you. Stock up on grenades from the crate and head around the rubble and up the stairs.

Poor Barney — he's been pinned down by the two snipers covering the building. His suggestion to take them out with grenades is a good one, so toss one in to the window with the sniper in on the left. The second sniper is a little harder to get because he's at the other end, plus there are two poison headcrabs. Use the gravity gun and filing cabinet combination to make a rudimentary shield from the sniper fire until you reach Barney's position.

Grenade the second sniper to make it safe for Barney to lead the way. Follow him down the stairs and out the side of the building. He'll unlock the gate ahead. Grab the supplies and head through the door on the right. There's a couple of poison headcrabs in the corridor ahead.

A couple resistance fighters will join you in the courtyard, but not before some combine soldiers attack through the door ahead. There's a sentry gun at the top of the stairs, but there's also a conveniently placed explosive barrel nearby.

It's supply central through the doors, with plenty of SMG ammo and medkits. Head up the stairs to the 2nd floor and take a look at the old museum from the window. That's where you need to go.

Barney will open the door, then follow him through to the next room. One of those pesky cameras (like the one that spotted you in the train station) will start photographing you. Strike a few poses while you can, because your male modelling session will come to an abrupt end when Barney shoots the camera out. He's just jealous.

Head downstairs, where you'll see a spider mine at the end of the corridor. There's a sentry gun just out of sight around the left hand corner, so watch out for that. Pick up the spider mine with your gravity gun and throw it around the corner, from a safe distance, to hit the sentry.

Before you head out on to the street, get ready on your sprint button. The suppression device Barney mentioned can target you on the street, and it does a fair bit of damage. The targeted ground will turn yellow just before it gets blasted, giving you a second to dive out of the way if you're targeted by it.

As soon as you get on to the street, turn left and run for the overturned blue dumpster. You can catch your breath quickly there, before moving around behind it to the far end of the street. There's a door on your left with a couple of Combine soldiers inside, taking these out shouldn't be too hard. There is a medkit station next to a closed door in this room, use it to replenish any health you need and then head out the door.

Once again it's a mad rush forward making sure to stay clear of the sentry gun's blast radius. Your next target is the bunker in the middle of the square dead ahead. Once you get close, be prepared for a combine soldier inside to start attacking. There's only one and you've just stocked up on health so he shouldn't be a problem. Take a breather in here until you are ready for your next mad rush outside towards the closed door.

There is a little surprise in store for you as two combine solders bust out of the door. Take them down and make your way hastily inside to save some captured rebels from an execution. After some cheery greetings and instructions from Barney, collect any supplies you need from here and free your new friends by bashing the lock off the door. They will grab themselves some weapons off the storage racks and join you in your endeavour.

Open the closed door and make your way towards the steps of the combine-controlled bank that Barney mentioned earlier. You'll meet up with some combine resistance here. Be careful though, there is an Elite who isn't afraid to use the secondary fire of the disruptor rifle. Once you have dispensed with these annoyances make your way forward once again. You should see a blue energy shield up ahead, move toward it and use your gravity gun to unplug it from the power socket. You can now lead your small party of resistance into the building.

Once you have climbed the stairs and moved into the building, the double wooden doors to your left are where you want to be going. Opening these doors, blue lasers, grenades, and a metal grate on the floor greet you. You'll want to stock up on some grenades so duck into the room on your right and bash open the supply crates or just grab some from the conveniently placed grenade stash. Moving closer to the blue lasers, Barney explains that they will trigger a sentry gun. Lucky for him you can't talk, otherwise you might get to disagree with his decision to let you deal with the problem. If you've managed to keep some resistance fighters and are cowardly, you can always order them into the lasers by using the "c" key. Staying close to the metal grating, walk though the lasers while ducking with your grenade out — you're going to throw one into the hole where the sentry gun pops out.

The sentry gun dealt with, Barney opens the door for you to enter the foyer of the building. Run in and collect what's inside of the supply crate laying on the ground here. After hearing some ships fly past, Barney will explain that your motley band of rebels will need to take out some generators in order to advance. Once you've digested this information, run around to the other side of the staircase, you will spot an open door protected by more blue lasers. Guess what's in store for you! Be wary of combine through the energy shield to your left, a grenade though to the end of this passage and some SMG fire should clean them out pretty quickly.

After walking though the blue lasers you will notice that there is another laser covering the first. Take out the first quickly, and use its raised platform to stay above the firing range of the other sentry gun as you throw another grenade at that. Your rebel pals should start to follow you into the room just in time to help you with the combine that are waiting around the next corner. Walk up this corridor and you will se a stairwell on your left, lead your party up here.

Once more, the blue lasers greet you, but don't trigger them just yet. Walk into the adjacent room to rescue some more of the rebels, once again they will arm themselves with whatever is available and join your cause. Take the time to grab what health you can from the available supply boxes and get working on those sentry turrets — there's one on each side of the doorway though which you can see the first of the generators.

In the room use the available resources to stock up on health and suit energy. Once you're done walk up to the generator to hear Barney's explanation of how to disable it. Once this is done, head out of the room and across the walkway, and you'll be greeted by more blue lasers. The good news is, you don't have to take this sentry gun out, you can just use the gravity gun to collect the supply crates stacked behind the lasers, however you will need to be careful for the group of combine that will come out the passageway to the right.

Going down this passageway, you will come to a room with lots of red lasers. Barney tells you that he'll let you go ahead and disable the security system before he will follow you though. This area requires you to do some climbing and jumping to get past the lasers without triggering them. It's rather easy if you use the following instructions. Jump up onto the ledge that is in front and to the left of you, turn left and you should see a block. Jump onto this, then use your height from this block to jump over the lasers on the ground to your right (if you're facing the wall). There is a cylindrical pole here, climb up to the top step and jump over the laser to the piping on the wall. Use the piping to climb up onto what looks like book cases. From the first book case jump across to the next, then duck and crawl forward sticking close to the wall. Dropping down, walk around to the other side of the doorway where you will find a button, press it and the security system will deactivate. Barney will join you but you may have to return to the start of the room to collect any stray rebel followers that you may have with you. Don't forget to stock up on the ammunition and health before you head off out onto the corridor.

Conveniently located in the door directly to your right, the next generator waits for you to disable it with your gravity gun. Once you have done this hurry back out into the corridor and help Barney and the rest of your friends take out the combine that attack from beyond the energy shield. Once you've done this, turn around and head though the red laser room again, be wary for another party of combine soldiers trying to sneak up on you.

After disposing of the combine forces and exiting the room, follow the corridor to the left. This will take you out to the foyer stairwell — the other side of the energy shield. Walking down here, more combine will enter the foyer, take them out using the balcony and your higher position to your advantage.

After dealing with these, follow the corridor around until you enter the large room with some hoppers and supplies. You will become trapped in here, so take the first few moments to raid all the supplies in the room that you can get. Combine will start to circle the room but you can easily take them out with a few well placed shotgun blasts though the breaks in the wall. When things quieten down, you may notice on the screen that some combine are opening the doors by force. Barney suggests that you set some traps so follow his advice and use the gravity gun to place a hopper in front of the two metal doors at the end of the room. You can easily take out the rest of the combine forces with the disruptor rifle after they bust in.

Once things have died down, grab any supplies that you need and head out the first door that the combine came though. You'll be faced with some more sentry turrets, take them out by sprinting though the blue lasers and dropping a grenade in each hole. With the sentry tunnels disabled, you can now go into the room on your left and disable the last of the energy shields. Barney will congratulate you on a job well done and tell you that your next objective is to get to the roof.

Follow Barney but be careful for yet another combine encounter in the foyer. After this Barney will lead you through the hallway marked exit. It's time for you two to part ways again, with Barney volunteering himself to hold the gateway to the roof open long enough to make a difference, don't worry though — he'll be forwarding straggling rebels to help you in your cause.

Make your way onward though the doorway that Barney has opened and up the flights of stairs, collecting any useful inventory along the way. Be prepared to encounter some light resistance in the form of portable turrets and a few combine soldiers. Reaching the top of the stairs you will come to the roof, giving you a nice view of a futuristic city in ruins after an invasion. Don't take too long to enjoy it though, because the roof is also swarming with combine. Take them out while using the available cover to your advantage, and don't forget to keep your eyes open for supplies scattered around the roof as you eliminate the combine forces, you'll need them for what's up ahead. Make your way towards the large RPG supply crate. You'll need to use this as your base restocking point as you take out the combine gunship that is circling the rooftop. Once again use the cover to your advantage, you can run back into the stairwell when the gunship is raining down machine gun fire on you then duck out to take a quick shot off while you still have ammunition available. Some of the surrounding supply crates should have left you with some spare rockets laying around as well.

After the gunship has been taken out, make your way to the gateway at the other side of the roof, it should open and allow a new wave of combine to attack. Don't forget that you can use your rocket launcher more freely because of the nearby supply crate. Once this new wave of combine have been eliminated, head into the newly opened area. There is an unbridged walkway that needs to be opened via the bright red button on the block adjacent to the closed gate. Press the button and hide from combine fire while the bridge is spanned. Once the gate to the bridge opens, run out from your hiding spot and use your rocket launcher to take out the large group of combine.

Advancing across the now cleared bridge, ready your shotgun for any remaining combine to be taken down in close quarters combat. From this room there is only one way out, and that's dropping down into the stairwell. Luckily your rebel friends will follow you down the jump. Continue downwards until you reach the ground floor, turning left will take you out into the courtyard in front of the large building you were just in. An RPG equipped resistance fighter will greet you along the way and explain the situation, there's a cache of rockets stashed in the courtyard and they need your help to take out the numerous striders that are patrolling this area. Get yourself ready for this by equipping your RPG.

Fast movement and good cover is the key for dealing with striders, when you're not under cover or directing a rocket towards a strider you should be sprinting for some decent cover. Luckily this area is littered with cover and RPG ammo. Make your way towards the front steps of the large building where a few of your rebel friends are attacking the striders from. This is a good place to get a few shots off before you continue onward for some more cover. Once you're ready to move on, strafe right and drop down behind the stairs, there's a combine vehicle adding extra cover, as well as a fallen rebel soldier with some health packs surrounding him. Take what you need from here and make your way around the vehicle towards the opened sewer. In here you are safe from strider attacks, but there is no nearby ammunition for you to raid so you will need to continue onwards. Coming out of the sewer, climb up out of the pit and make your way into the centre garden area and toward the semi-underground covered area. There are spare RPG's laying around in here for extra ammunition, and some good cover as well.

Once you are ready to move onwards continue in the same direction you were going and turn right to get out of the courtyard area and you will see a small entrance to an undercover walkway with plenty of rubble built up for cover, make you way into here. You will find the cache of rockets and some allies will drop some health packs for you. Take what you need and eliminate the rest of the striders. You will have plenty of cover and help from allies in this position. Of note is the hidden room that can be blasted open by strider fire near this area, there is ahealth dispenser in here and you can also use it for extra cover.

Once all the striders have been taken care of, you can make your way toward the combine blockade. By this time you should have cleared out all the resisting combine forces so this area should have some ammunition for you to pick up. Find the tunnel entrance to continue onwards, there are some supply crates down here that you may want to raid before you continue on.

Coming out of the walkway tunnel you will find yourself at the end of a collapsed traffic tunnel, make your way towards the open end and use your crossbow to take out the single combine soldier firing at you from the mouth of the tunnel. Don't forget to deal with the scanners that hover around here either. From here you will need to sprint forwards to keep away from the strider that has busted though the blockage behind you. Stick to the left side of the tunnel so that you can run to cover as soon as you reach the tunnel mouth. There is a broken wall here that you can use to gain access to the abandoned building, enter though here and prepare yourself for the combine soldiers that will storm at you from the stairwell. After eliminating this force, climb up the stairs, there is one combine soldier waiting for you behind some cover at the top here, a well placed grenade should be enough to take him out. In the bathroom on this floor there are some supply crates, there also seem to be an abundance of scanners flying about here, so make some use of your gravity gun to get rid of them.

From here you will need to make your way to the stairwell on the top floor. You cannot reach this from the third floor however, because the stairs have collapsed in this location. This however is rectified by a strider blast to the building when you reach the third floor, a support beam falls allowing you access to the top floor. From here make your way across the support beams to the stairwell where the cache of RPG ammo is located. Using this and the ample cover from rubble on the top floor, you should have no trouble taking out the strider.

Your strider problems now gone for the moment, restock on RPG ammunition at the cache and make your way though the clear hallway here. Collect any goodies in the supply crates along the way. Take the first left and drop down the hole in the floor here. Continue on and break through the wood blocking the way though the break on the wall, you will run into a resistance member who tells you that you're going to have to try and make it to the citadel wall. With your new friend following you rush forward into the hole in the ground. Using the cars as cover, take out the combine forces that attack you in this old car park and collect any goodies that you may find lying around then head out the conveniently placed ramp of rubble while watching out for the combine elites that will try to intercept you as you walk up the ramp.

Once you've reached the top of the pile of rubble, head forward and left for a tunnel opening in the middle of the road. The tunnel is short, but it will serve as good protection from the strider that takes up residence on the road above you. Use the two mouths of the tunnel to get behind the strider and unleash all your available rockets from there. Moving onwards, run out of the mouth of the tunnel with the flames being careful not to get burnt — you're going to need all the health you can get up ahead. There's an open shop that you can use for temporary cover while you wait for the strider to turn away so you can head off again, don't forget to raid the storage crates in here.

Running on down the street you come too what looks like a dead end, until another strider busts though and clears the way for you. There's a small alcove to the right in the shopfronts, use this as cover while the strider passes you by, then sprint into the freshly opened hole where the barricade of cars used to be.

Combine radio chatter and a beeping sound are all that greet you in this new area, be careful — that beeping sound you hear is explosives ready to be detonated by the combine who will attack immediately after. Use the pulse rifle and the surrounding cars to your advantage to take the combine out. Right on cue, some resistance forces will find you and offer to lend a hand in your cause — visit the medic for some health which you will probably need. When you're ready continue through the underground area and make your way up another conveniently placed pile of rubble.

You'll find yourself in the middle of a ruined building with combine forces all around. You should be able to deal with them with help from your resistance allies, but be careful for the striders that are pacing around the building outside, they can use their weapons to break though the walls and attack you and your allies from here. Use what little walls are around for cover from these attacks while continually moving forward — you'll soon discover a door leading to a darkened room, head in here for a quick break while you raid the two storage crates in the lit room here. When you're ready continue up the stairs to the second floor.

There's a strider directly in front of you, so duck behind any cover to avoid getting hit here, your target is the doorway ahead and to the left, where a pile of rubble leads back down to the first floor. Keep holding off the combine fire while you are down in this area — you're waiting for the striders outside to break a new pathway in the walls for you. When this happens, move through and jump down to the lower level. To your left there is a room with some supply crates for you to raid.

When you're ready, head up the rubble pile to be greeted with more combine fire. Take out the combine elite who is hiding behind the half destroyed wall to your left, and take what you can from the supply crates nearby. At the half-ruined wall you'll need to turn left again and head into a tiled area. Be careful for combine and strider fire and you should make it to the mother load of all stashes. Two health dispensers, a suit dispenser and some supply crates in a nearby room greet you in this area. Take what you need while doing your best to avoid enemy fire. When you're ready head up the stairwell at the other end of this area.

You've reached the top of the building, and your staging area for the next attack on the striders. Take out any combine soldiers that you see on this level and stock up on RPG ammo from the cache. You'll need to find a well hidden spot from which you can attack the striders, the best of which in the middle of the room where the floor has been broken down, duck in the lowest part here and you should be safe from strider fire. Be patient and use the surrounding cover well especially when restocking your ammunition and you should be able to down the striders that surround you.

Once you've done this, your allies will tell you that you need to head off towards the horse in the square. To do this, make your way along the metal supports and towards the road. Once you've reached the edge of the building, drop down onto the dumpster, and again onto the street. You'll run into some more combine resistance, but if you've made it this far you should have no difficulty pushing forward until you run into Barney and Dog.

Barney explains that Dog thinks Alyx is in the Citadel, and he doesn't know what to do. When you're ready, join Barney and Dog at the citadel walls. When you get there, Dog will lift up one of the sections of the wall to allow you to drop down the newly opened hole and enter the citadel. While you're falling, listen to Barney's instructions for what to do when you meet Dr. Breen.