Part 35

Drop down, go up steps, and enter a room with three scientists.

Cross the adjacent room, jump across the left side when safe, and use the sparking control panel to shut off the "surgical unit."

If the unit blocks the walkway, turn it on and off again until clear.

Use the blinky-light panel to open the doors.

Talk to a scientist to have him follow you.

Exit the surgery room, turn left, and lead the scientist through the hallway with broken headcrab cages. Talk to him again if he stops following.

Go past the cages back to the lobby.

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

Approach the retinal scanner to the right of the lobby's exit doors and wait for the scientist to unlock them.

Use the nearby HEV station if needed, then go through the doors and turnstile to reach section c2a4g.

When the outer doors open, crouch-walk through and stay near them as they close.

Sneak-shoot a nearby marine with the .357.

Go to where the dead scientists are, turn around, and look up at the top of the nearby wall.

Shoot down the first turret from a distance with the pistol.

Move back to see and shoot down the second turret.

Turn and shoot the explosive crates blocking the path.

Go past the crates to find more crates with armor batteries and .357 ammo.

Go up to the big door to start the "Surface Tension" chapter.

Use the button panel to open the door and run through before it closes.

Quickly pistol-sneak-shoot the marines around the corners ahead.

Use the assault rifle and an AR grenade on the next two marines, or shoot explosive barrels first. Alternatively, sneak-shoot with the crossbow or toss snarks.

Check for health packs and return to the armor battery location if armor is less than 100%.

Approach the dam and shoot the sandbag-protected mounted gun with the assault rifle until it blows up.

If you're fast, you can avoid the chopper. Otherwise, duck for cover.

Wait in a dark corner for the chopper to potentially kill the ichthyosaur in the water. Quicksave and check periodically, quickloading if the ichthyosaur is still alive.

Alternatively, finish off the ichthyosaur with the shotgun/assault rifle, staying in the water's corner to avoid damage.

(Optional) Destroy the chopper with two fully powered gauss gun altfire blasts before entering the water.

Dive into the water next to the dam and swim to the small tower structure.

Climb the ladder on the tower's side.

Use the first aid station if needed, then use the button panel to turn its button red.

Quicksave, dive into the water, and locate the valve wheel on the dam wall with a red light nearby.