Enemies: 5x Arch-Ville, 27x Cherub, 19x Imp, 28x Trite, 13x Wraith, 6x Zombies

After a cutscene (a non-interactive cinematic the game plays automatically), leave the bay door and follow the hall. Near glass, 2 Imps will be summoned; kill them both.

Enter the room and find a cabinet with a Rocket Launcher (code: 571).

Kill the Wraith and 3 Cherubs.

Head towards the door with the big red arrow.

Go the opposite way of the red arrow door, where 2 Cherubs previously appeared.

An Arch-vile will be summoned near the locked door. Kill the Arch-Ville and any encountered Cherubs.

Return to the door with the arrow. Check the 2 small rooms on the way; one has goodies, the other an Imp.

Another Imp will be summoned near the door with the arrow; kill it and enter the door.

Enter the next room and then the door.

Upon entering this room, 2 Imps and a few Trites will appear. Kill them.

As you move to the other side of the room, a Commando-Zombie will be summoned in the previous room; kill it.

Another Commando-Zombie will be summoned on the other side of the room; kill it.

Look for a panel to view cameras. Select the second choice, and a Trite will appear. The third choice shows a meeting room and the code 627.

Use another panel in this room to open a hatch containing a PDA.

Return to the Lab A door. A few Trites will attack on the way; kill them.

Enter the code 627 and enter the new room. Go right, avoiding the lava on the left.

Cross the room and enter the door.

Inside, 5 Cherubs, 2 Imps, and 1 Wraith will appear; kill them all.

Grab the goodies and enter the next door.

Grab more goodies by jumping, then return to the previous room.

Kill the 2 Cherubs.