1. Walk through the open doorway. Dog will follow.

2. You soon learn that Dog is an insurgent's best friend.

3. He clears a path for you, eliminating all Combine forces in your way, then opens this roadblock for you to enter.

4. But soon a Combine airship approaches, then flies off - carrying with it a very determined Dog.

5. The way out is over this fence and into the building.

6. Amazingly, this zone is already spent. Climb over the debris to load the next area.

7. Exit the building out the other side and encounter this friendly chap, playing skeet with camera drones.

8. Farther along are these three rebels, freeing the neighborhood of Dr. Breen's rants.

9. This capable quartet is now yours to command. The interface alerts you to a new control set. Hit the key once to station your squad where your crosshairs are. Hit the key twice to recall them.

10. A pair of Combine troops enter the plaza next to the souvenir shop. You may need to walk the block to trigger this sequence. Grab the health kit from the supply crate on the left.

11. Continue where the Combine emerged then ascend these stairs to load another zone.

12. Use your gravity gun to remove this metal sheeting from the hole below. Be careful not to fall in.

13. Inside are these pop-up mines, called hoppers. Use your gravity gun to disable them. Secondary fire will pick one up. Wait for the color to change from red, to green, to blue. You can then safely set it back down and it will again light green. Once all the hoppers glow green, jump down the hole.

14. Supplies, and another hopper, are inside this shed. If you are patient, you can lure a head crab into the hopper's trigger zone.

15. A medic joins your squad through this tunnel. He will heal you and your troops as you take damage. To the right is this strider -- impervious for now.

16. To the left is this combine sniper. Turn the tables on him with your crossbow.

17. Continue up the road, clearing out head crabs and hoppers.

18. Enter this alley on the right. Beware two hoppers on the ground plus the Combine trooper in the window ahead. Another CP will emerge from a window to the left.

19. Clear out the troops and hoppers in the area, then move this barrel and metal plate to find supplies. More supplies are in a shed at the other end of the lane.

20. Descend some stairs then toss a flammable barrel or two at the CPs in this courtyard. Supplies (and another CP) are in the shed at the far end.

21. Continue through this doorway to load the next zone.

22. Ascend the stairs for this small diversion if you'd like to fight a zombie and listen to Dr. Breen on TV.

23. Outside, a strider and an impassible crater are to the left. This medkit and medic are to the right.

24. Continue through this doorway.

25. Bust open these supply crates before ascending the nearby stairs.

26. This gunfight ensues past the second flight of stairs. I lost a couple squad members in this fight, but to be honest was relieved because they were mostly in my way in these close quarters. Note the supply crates on the right.

27. Even if I send the NPCs away, they eventually crowd around me like this. Very annoying. Note the medical station on the wall. A supply crate with energy is in the next room ahead, and ammo is on the table to the right.

28. Your crossbow is the best weapon at range. Zoom with secondary fire then drop your target with primary fire.

29. Two turrets are below. Before jumping down, explode this barrel and with any luck you'll topple both. Also below is a medical station.

30. Exit right. (If you exit left, you'll be on the wrong side of the crater you couldn't pass earlier.) There is an infinite spawn of CPs that come pouring out of the building at the end of the lane. Don't waste your ammo on them. Instead, rush to the indicated doorway.

31. Inside are more CP as well as several hoppers. Fight your way up the stairs to this room where you'll find these supply crates with suit energy. Drop through the hole to the floors below.

32. Take the outside door and emerge here, where you can drop this sniper for a very cool example of rag doll physics.

33. Climb some stairs then use the indicated switch to open a small gate in the barricade, allowing any team members trapped on the other side to join you. A medical station is just behind the switch.

34. Continue up the catwalk and enter the building, where more CPs are holed-up inside. Note the energy station on the right. A crate with ammo is in the next room on the right.

35. Don't go up the stairs -- the only thing up there is an automated turret. Instead, go down the stairs where you'll find more ammo supply crates. Another firefight awaits you in the hallway outside.

36. Descend these stairs to another firefight, where manhacks will join the CPs in the hallway. Peer through the locked gate visible ahead to spy a lambda and supplies, inaccessible for the moment.

37. Descend another set of stairs then ready your gravity gun before entering this room. In addition to the dual turrets visible far-left, a third is around the near-left corner. Note the health station and supply crate.

38. Continue through this hole in the wall, but beware the zombie lurking within.

39. The hallway on the left loads the next area, but before taking that route head up these stairs first.

40. Find the supply crates you spied earlier. Your gravity gun can lift them up and over the fence. Inside are energy and ammo. Now return to the corridor and load the next zone.

41. You emerge in this tunnel for the mother of all manhack battles. Rather than burn lots of ammo, use your gravity gun to grab the manhacks then toss them to an instant death. It's also wise to pull back and let your squad engage the manhacks, as this is probably their best use in the game.

42. Arrive at this area by keeping right past an overturned truck, then climb the rubble ahead to clear the fence. Unlock the gate on the right so your squad can join you. (You can just pick up the lock with your hand.) Continue through the door ahead after opening a supply crate off-scene to the right.

43. Another manhack attack. Again, your gravity gun works well.

44. Open the supply crates to the left before opening this door. Outside are more CPs. Your squad is vulnerable at this doorway so I found it was best to actually send them behind myself while I took point.

45. At the far end of the tunnel is this CP manning a turret. Your trusty Magnum takes him out in one shot.

46. Approach that hole and you are recognized by a medic on the other side. He offers to blow a larger hole in the wall.

47. Before that happens, though, more manhacks and CPs attack. Man the nearby turret and finish them off while you wait for the explosives. Once clear, head through.

48. Your squad will gather around this door. If you try to open it, they'll tell you that it's locked from the other side, but that you might be able to find a way around. Continue through this crawlspace (inset).

49. Smash open the crates for energy, then climb onto the truck ahead.

50. Toxic sludge covers the ground below. Use the now-familiar technique of using two crates and a gravity gun to step across the sludge.

51. Several zombies will slow your advance, especially once you get to this middle ground.

52. A medkit can be found here on the right.

53. Make your way left to this white car. Climb over it then ramp up the pipes along the wall.

54. Smash open one of the grates on the right then enter the vent. Smash another grate to drop below.

55. Bust open these supply crates, then open the previously-locked door on the right so your buddies can join you. Ascend the stairs across from the door to load the next area.