This is another great level, with a nice layout and interesting objectives. There are three main objectives in this level, some with multiple parts.
Fluid processors[edit]
You begin inside a teleporter in a small room. On either side is a door; both lead to identical rooms with Skeevin spawn-chambers and constructs in the middle. A larger hallway connects these two rooms, and a forcefield blocks another corridor at a T-junction. Up on the central constructs in the two rooms are switches. If you're able to, save some of those ammo crates. In each room, jump onto an ammo crate, then to the Mazrium platform, then up to the platform on the construct, and hit the switch. If the ammo crates got destroyed (easy to do when the Droppers explode) it's no big deal, because you can jump from the shelves with the spawn tanks. It's just harder is all. When you've hit both switches, this objective is completed and the forcefield in the hall is deactivated. In the connecting hallway, look for a misaligned texture on the wall approximately opposite the forcefield. There's a secret area inside.
Contamination[edit]
Go down the corridor past where the forcefield was, to where it T-junctions again. The next objective is to the right, but go left first for a bonus area. There's a big room here with specimens in tanks along the walls, and two chambers near the middle of the room with glassed-over entrances. Stand way back from each entrance and shoot the glass. (Look inside first and you'll see why.) In one chamber is a switch high up and almost out of sight. Jump and hit this switch--keep trying and you'll get the timing right. This uncovers a door to a secret area next to the main door to the room.
When you're done here, go back to the corridor outside and take the other way (that slopes down) to a room with a bunch of pipes. There are two ways to go from here: the left way goes to an elevator. Go to the right, to a room with a biogen-fluid pool and a lower side room. Enjoy sloshing around in the nice clean biogen fluid if you like, because you're about to make things a bit icky. Hit the switch in the side room to contaminate the biogen fluid and complete the second objective. (Look at the automap while you hit the switch if you want to watch it go dirty.)
Five-part lock[edit]
Go back to the pipes room, and down the corridor on the opposite side to a very cool elevator. Go down and to the big central room. In the middle of the big platform is a floor plate. Step on it, and those five small doors in a row on the wall will open. If you look up close you'll see unlit lamps inside. Each of these corresponds to one piece of the lock, and will light up when that piece is released. The various pieces are in side areas off this main room. You can do these in any order.
Piece 4[edit]
To the right is a low channel with black sludge. Shoot the switch to start the Mazrium platform cycling, and take it down to a big sludge-filled room. It's tough to deal with both the Roto-droid and all the Gryklaan (how can they stand that black crap?) at once, so just make a run for it and take cover behind the console. The switch in here releases Piece 4.
Piece 2[edit]
Go through the door in the main room; this leads to a network of corridors. To your left appears to be a dead-end. It's not: at the end is a hidden lift that goes down to a secret area. Take the right-hand passage to a laboratory. The switch in here releases Piece 2. The door only opens from the outside, so go down that conveyor, which leads to a teleporter that itself goes back to the main room. Watch out for the Roto-droid in here--try putting a Missile Hunter-Killer and Detonation Mines on the conveyor and setting them off when they reach the room at the end. Before taking the teleporter, hit the shootable switch nearby. This opens that small door next to the lamps back in the main room. There's a secret area inside.
Piece 5[edit]
Go to the corridors, and down the sloping one to where it T-junctions. In the room to the left is a pool with contaminated biogen fluid. Hit the switch in here to release Piece 5. (This looks like it was contaminated when you completed the second objective, but actually it was this way the whole time.)
Piece 1[edit]
Go the other way in the corridor to a tall room with black sludge down below. Shoot the switch directly ahead on the central column to start up the Mazrium platform. There's a bit of a puzzle here. There are two small doors up on the wall to your left when you came in. In the right-hand one is a small room with the switch that releases Piece 1. To open this door, ride the platform around and shoot the switch on the ledge that was to your right when you first came in. Don't hit it too soon, or the door will close before you're close enough to jump to it. The teleporter inside goes back to the main room.
There's also a very important secret area in here. On that second ledge diagonally opposite the entrance is another small door that doesn't open normally, plus there's a door going through the central column that doesn't seem to serve any purpose. First, ride the platform around to the far side of the column from the lock-piece-door switch. Then shoot at the door in the column to open it, and shoot the lock-piece-door switch through the doorway when you're lined up (or shoot the switch just before you go around the column). In addition to opening the lock-piece door like usual, it also momentarily opens that door on the second ledge, inside which is yet another shootable switch. Now, quickly adjust your aim and shoot that switch before you move around the column. This last switch opens the left-hand door up on the wall, the one near the entrance to the room. You'll need to wait until just before the column is in the way, otherwise the door will close before you can get close enough. (You may need a few tries before you get it.) Once you get into that left-hand side room, look for a misaligned texture, and a tiny gap at the floor (it's behind the full-health). The secret area is in here, and contains a Secret Level Access Keycard. It connects to the lock-piece room through a hidden door.
Piece 3[edit]
In the main room, go down the passage to the left of the lamps. This is the "gauntlet," portions of which are a real headache. Just quick-save your game a lot, to cut down on the irritation factor. The first of three parts is easy enough: destroy the wall emplacements. The second part is a series of crushers. The easiest way to get through these is to face sideways and strafe through one at a time. You might want to turn off speed-lock to keep from overstepping. Watch out for the launchers on the ceiling between the crushers. The third part is a series of precise fatal-if-you-miss jumps. By the highest platform, to the right, there's a hidden door with a secret area inside. Around the corner past the jumps is the switch to Piece 3. It's guarded by a Roto-droid so get a suitable weapon ready. The teleporter nearby exits back to the main room.
Solving the lock[edit]
When you've released all five pieces, go to the main room. Get a big weapon ready, and step on the floor plate. On guard! The whole platform sinks well below the floor level, like an orchestra pit. Except you won't be playing music down here, but fighting Roto-droids! This is a good place for a Death Sphere if you have one, because there's that one in the secret area along the Gauntlet. (Sort-of sneaky tip: after activating the floor plate, immediately jump clear of the lowering platform. Needless to say, it's much easier to fight the Roto-droids from above.)
After defeating the Roto-droids, the platform returns back up to its normal position. You've completed your tasks in this level. A hidden door has opened here in the main room, with the level exit inside. If you're going to Gateway (B6) and not the secret level, gather all the items you can because that final level is quite difficult. When you're ready, take the exit elevator to the next level.
Secret Level Alert[edit]
This episode's secret level is accessed following this level. If you have collected five Secret Level Access Keycards thus far, you'll go to Biolab Conduit (BBonus) next. Otherwise, you'll continue to Gateway (B6).