1. Emerge here and be joined by another medic. Ready your SMG, as a rocket soon arrives, unleashing a swarm of head crabs. Continue through the alley ahead/left after grabbing the supplies on the far side of the van.
2. Bust open this supply crate for some ammo then head left after this chap warns that its too dangerous for you here. Yeah, right.
3. Beware this head crab at the top of the stairs. Bust through the planks blocking the doorway on the left.
4. A firefight between the Combine and the underground rages outside. You can help take out the Combine from these windows, but shooting between the bars is a pain. I skipped it and just rushed through the house.
5. Drop through here then grab the supplies before continuing.
6. Grab the grenades from the counter on the right before descending the stairs.
7. You're now on the other side of this fence. Look up to witness an amazing rag doll sequence.
8. Snipe an Overwatch on the roof, then head into this door after your buddy reveals the password, "password." Check.
9. Beware this Overwatch who comes charging down the stairs. Energy and ammo are in the room on the right.
10. Fight your way up the stairs then down through this hole.
11. After finishing off this Overwatch and grabbing the ammo from the crate, step onto the ledge and a comrade will extend a catwalk for you to cross.
12. Once your squad is across, pull this lever to raise the catwalk and stop your pursuers. Note the falling Overwatch in the background.
13. Continue through here, then up some stairs to a swarm of head crabs.
14. Turn right to be confronted by this very fast toxic zombie. A medkit is in a bathroom around the corner.
15. To the left is another hole for you to drop through.
16. Battle more zombies and head crabs then emerge here. The stairs are blocked by a rocket. Grab the medkit ahead then follow the hall on the right to supply crates.
17. A battle follows in this courtyard. When fire is coming at you from multiple sides, the seemingly obvious suddenly becomes invisible. I was oblivious to the hopper at (1) and to a grenade-tossing Overwatch at (2). My preferred weapon in open areas like this is the crossbow, which worked well. Continue through the door at (3).
18. Find a medkit (and a head crab) then climb the debris left to more squad mates. Grab the supplies and exit through the opening ahead.
19. There are lots of grenade-tossing troops on the neighboring buildings. Keep your squad inside until you snipe the Overwatch with your crossbow. Release the crank ahead to drop the catwalk.
20. Don't be in a hurry to hop down that hole in the floor. Take the supplies on the right, then do your best to snipe any Combine through the hole. Ready grenades or your SMG if you have SMG grenades before dropping down.
21. Charge in full-bear and do your best to take as many down as quickly as you can, trying to avoid losses as your squad quickly follows in behind you. Supply crates are behind you, and more Overwatch will attack from the right.
22. Enter the corridor on the right and more Overwatch drop in from above after exploding a hole in the ceiling.
23. Push to the rear of the building, taking out these two Overwatch. Note the health kits on the ground. Continue up the stairs on the right, but be careful of a barnacle on the ceiling.
24. Continue up a second flight of stairs then turn right into this room. Beware another barnacle and this toxic zombie, here pouncing on my squad mate. Drop through the hole in the floor visible ahead.
25. This horrific scene follows. Finish off the zombie and Overwatch here. Toss a grenade or two into the hole on the left before dropping through. (I didn't and lost two squaddies.)
26. This area is a bit disorienting. The lambda is your immediate destination. Note the fire on the right for reference.
27. More supply crates are past the fence. Like before, use your gravity gun to lift them over the fence. A stairwell to the left leads to the next zone.
28. Grab the supplies at the top of the stairs then enter yet another room with a hole in the floor. You can toss a grenade to topple the two turrets (battling a zombie and a head crab) but there are health and energy stations below, so my preference is to save the grenade and get up close with the gravity gun.
29. After a moment, Alyx busts through the door.
30. Fight your way to the stairway ahead. Note the health and energy stations on the wall.
31. Defeat a solitary overwatch on your way down the stairs, then Alyx tells you to take one door while she takes the other.
32. Bust through the door and Alyx charges in synchronicity. This is what I prefer to use grenades for. Make sure Alyx doesn't die. Otherwise, your employment is terminated.
33. Once the room is secure, Alyx explains the plan and more squad mates join you. Continue through the door ahead.
34. You might want to save your game before exiting out this door, and fill up on any health and energy left from the previous stations. The next sequence is pretty tough.
35. The exchange begins pretty easily. Use your crossbow to snipe this CP as well as a sniper above. Note the hopper atop the supply crates.
36. Alyx works on dropping the generator's shields, which is behind me in this shot. The medic is shooting at a manhack. Don't miss the medical station here.
37. It starts to get hairy as a pair of drop ships deliver more troops. They'll come at you from this lane on the right and from another on the left.
38. Note the CP on the balcony ahead.
39. Nailed him to the wall! Love the crossbow.
40. The AI here is pretty impressive. They'll use cover effectively, being cautious until they overrun your position in numbers. Try to push into their territory before they have a chance to build up in force.
41. Use grenades, rockets, whatever you've got to keep their numbers manageable. You'll know how far along you are as Alyx reports her progress. First the outer shields drop, then the inner shields.
42. Once Alyx tells you to hit the generator with your gravity gun, this is your target. I've just hit it and Elite troops can be seen attacking from the left. Time to run!
43. Turn around and run to this position, where Alyx will close the gates. Whew. I ran this sequence several times and this was the most health I was able to escape with. Its tough.
44. Alyx then makes an impressive climb to the roof of this building. Where she is knocked unconscious.
45. Use a barrel to reach the crate at (1) with your gravity gun. Inside is a medkit. Another medkit and ammo can be found at (2) before continuing through the doorway at (3) to load the next area.
46. Use your gravity gun to move the board holding this door in place. Drop into the hole ahead and repeat the procedure on the next door.
47. Zap these boards out of your way.
48. From the left comes a manhack attack. Secondary-fire grabs the manhack. Primary-fire tosses it into the wall for quick destruction. Most satisfying.
49. Your gravity gun is getting quite a workout. Use it to topple the barrels propping up this ramp. Clear the boxes away and climb across the ledge to the pipes above. Make sure there are no barrels under the ramp or else you won't be able to climb up it.
50. More manhacks attack. Defeat them then make your way into the ventilation grate ahead then drop out the other side.
51. More manhacks attack down this dead-end. At the back is health and energy.
52. Head right and come to these catwalks where Overwatch are firing at a zombie. The crate on the left holds a medkit.
53. Drop to this lower catwalk to battle a second group of Overwatch. A room to the right holds health, energy, and a toxic head crab, plus it's the way out.
54. But first, a brief but somewhat frustrating jumping puzzle, jump to the indicated ladder. From the ladder, drop to the ledge then grab the health, energy and ammo in the supply crates.
55. Back in the room with the toxic head crab, aim your gravity gun through the fence and lift the bar holding the door shut.
56. Ready your SMG for this next area as there are plenty of enemies: Overwatch, zombies, head crabs, toxic head crabs and barnacles.
57. Follow the corridor to the back then up a flight of stairs and past a toxic head crab to these medkits plus an energy cell and grenades. You'll have to use your gravity gun to pull them towards you.
58. Jump off this ledge. Ahead you can see a barnacle tongue and a toxic head crab.
59. Down here you'll find head crabs and zombies, plus a medkit far-left. Proceed through the doorway on the immediate left.
60. The ladder on the right is the way out, but for those who like a challenge there's an optional diversion ahead.
61. This extremely nasty toxic zombie and his many nastier toxic head crabs lurk within. I actually emptied my SMG in here. Note the lambda on the right, and the supplies in the shaft beneath. Use your gravity gun to pull the supplies out.
62. A normal head crab is ahead plus many ammo crates are at the end of the corridor. Another ammo crate is to their left. Now you can head up the ladder.
63. Surprise. More head crabs and ammo crates are up here, too. Move the barrel on the left (beware the head crab) and continue down the hallway where you'll find more supplies.
64. Yet more supplies can be found here. Ramp up the indicated plank to reach the catwalk. Save your game, as there is some nastiness coming up.
65. Ready you pulse rifle before crossing this catwalk. A trooper above drops the grenade at (1). Back off because the catwalk is about to split. You'll still have an easy time making it through the broken gate ahead, but beware the barnacle at (2). Enter the office at (3).
66. Look up. Take out this Overwatch trying to snipe you. Fill up at the health and energy stations, then grab the supplies (including crossbow ammunition). Ready your crossbow and activate the lift switch (inset).
67. This Overwatch immediately appears on the beams above. Snipe him with your crossbow. (Secondary fire zooms as seen here.)
68. Take pre-emptive action against the flammable barrel on the lift, and another Overwatch attacks from above. Snipe him with your crossbow, then refill your crossbow ammo, health and energy. Once the lift is in position, throw the switch to send it moving back and hop on.
69. While the lift traverses the span, you come under fire from more Overwatch. They are at some distance so again your crossbow is the weapon of choice. Hop off the lift once it reaches its stop.
70. Collect ammo from the fallen Overwatch then climb the nearby ladder (inset). An attack from these Elite Overwatch ensues. Nail them with your elite crossbow.
71. Step on to the mechanism above the lift and ready your crossbow. Once you step onto the rail ahead, another Overwatch is going to enter the lift control room. For an added challenge, see if you can snipe him before he activates the lift (inset).
72. Follow the rail under this catwalk then climb over the indicated railing to the adjacent catwalk.
73. Work your way to the indicated ladder and more Elite Overwatch attack. They'll fire deadly orbs that must be avoided (inset).
74. Climb the ladder all the way to the top and find two medkits plus ammo - and flammable barrels. If you're quick, you can pick one up with your gravity gun and throw it at the overwatch that attack from the balcony across the way, which is your ultimate destination. First, descend the ladder one level to retrieve a supply crate beneath you, plus the two visible ahead, plus more under a lambda to the left of the rusty office.
75. Lastly, Drop to the balcony, removing this hopper before continuing through the blue doors. Descend the stairs and remove another hopper to finish this long level.