Part 34

Sneak-shoot surviving marines, preferably with the pistol to conserve .357 ammo.

Ensure all enemies are dead, then collect any armor batteries and weapons from the marines.

Return to your security guard and escort him back to the computer room.

Proceed past the computer room to a winding hallway.

Sneak-shoot the marine at the left end of the hallway with the .357.

Move down the hallway to a door on the left.

(Optional Shortcut - Not Recommended) Move against the door and use the "Use item" key to activate the panel on the other side. Go through, shut off the "surgical unit" using the control panel, get a scientist to follow, and retrace steps to the lobby. This skips the gauss gun.

Continue down the main hall to a room with several crates.

Break all crates with the crowbar except the one with a tripmine aimed at it. Collect bullet clips and use the first aid station.

Return to the hallway path split and go the other way to find headcrab cages.

Run in front of the cages until the headcrabs break the glass, then move to a safe location and use your pistol to shoot them.

After all headcrabs are dealt with, go past the cages to doors leading back to the lobby.

Check the lobby's side hallway for a marine and shoot him if present.

Use the lobby's HEV station if needed.

Return to the headcrab cage area and go up the stairs between cages to reach section c2a4f.

In section c2a4f, move near the top of the second set of stairs and wait for marines fighting bullsquids to stop.

Peek around the corner with the crossbow in zoom mode. If a bullsquid is near a large crate, shoot the crate with the pistol to let the squid attack its target.

Shoot any visible marines in the head with the crossbow.

Move forward to an open doorway on your right.

If a bullsquid is present in the room past the doorway, sneak-shoot it with the pistol.

Continue down the main hall, watching for marines at the other end.

(Alternative Strategy) Peek around the corner at the top of the stairs to draw a marine's attention, then retreat down a few steps and use the shotgun. The marine may engage a bullsquid in a side room, allowing you to charge or wait for them to come within shotgun range.

Near the end of the main hall, check the room on the right for marines and break boxes outside it for ammo.

In the marines' room, pick up ammo boxes from shelves and use the first aid station if needed. Press the big red button on a panel to start a laser.

Down a side corridor, find a similar room with houndeyes. Kill them quickly with the assault rifle or shotgun, then press the room's big red button to start its laser.

Return to the main hallway and find another branch to the right with explosive crates.

Move into this side hall just enough to hear distant voices, then stop and wait for the guard with the experimental weapon to overcharge it.

Go down the side hall and into the room beyond. Pick up the experimental gauss gun (tau cannon) from the floor.

Find and use this room's big laser-starting button.

Return to the main hallway and go back to the room where you previously dealt with a bullsquid. Collect armor batteries from the shelves if needed.

Press that room's laser-starting button.

Go back down the main hall to the primary laser room.

Push the movable crate to obstruct the laser shield when it lowers.

Press the big yellow button on the nearby console to fire the laser and create a hole in the wall.

After the laser stops, go to the hole and crouch-walk slowly to drop onto a small metal ridge against the wall below the hole.

Walk along the ridge to the corner and drop onto a square joint on a vertical pipe.

From there, drop to the next small metal ridge against the wall, then to a curved section of pipe below it to reach section c2a4e.