Work your way back topside to meet Jan and the Crow. An exhaust venting port should lead to the outer hull of the cargo ship.
Mission Objective: Enter the main cargo hold.
Exit the hangar through one of the large diagonal doors. Continue through the next couple areas to the huge door that opens up into the cargo storage area. Go through the door to the left and down the ramp ways, and through the next few doors to the elevator; take the elevator down into the main cargo hold.
Secret Area 1/4: Step off of the elevator and continue forward, around the left side of the crate ahead. Turn right and run behind the crate until you reach the secret area to the left.
Proceed to the conveyor belt and hit the switch to disable the energy barrier, then jump on top of a passing crate and ride it into the magnetized hold.
Secret Area 2/4: Stay on the crate until it rounds the first corner (in the back of the hold); jump off and into the cubbyhole.
Secret Area 3/4: Jump onto the lowest magnetically-suspended crate, then from there to the higher one to the diagonal right. Jump from the crate to the ledge ahead. The back wall of the crate can be destroyed.
Secret Area 4/4: Backtrack to the very top crates and run along them in the opposite direction of the catwalk until you see a ledge below. Look for an armor vest.
Mission Objective: Manipulate the catwalks around the exhaust venting port to work your way topside.
Make your way onto the catwalk and enter the control room to find the blue key. Exit the room and jump onto the left-hand ledge with the crate sitting on it, then go through the door. Once inside, take the circular elevator in the center of the room to the floor above.
Pick up the yellow key off of the fallen officer and locate the lift trimmed by white lights. The lifts are a bit difficult to distinguish, and look like dark metal with slats in it. Ride the lift to the first stop and pick up the red key, then return to it before it leaves. Ride it all the way to the top and pick up the green key. Run across to the next shaft and call the lift, and then ride it down until it stops.
There is a switch on the wall; hit it to bring the catwalk over. Open the door and run across to the next room, then locate the next switch. Continue activating switches and running across catwalks until you make your way to the top of the venting port. Ride the final lift up and snake around the ramps, over the small wedge and down the next set of ramps. Across the bridge and around the ramp way is a door leading to the shell of the venting port.
Mission Objective: Return to the main deck and look for the Crow.
Climb the slope to the circular walkway above and locate the small bridge leading to the door. Go through it and ride the elevator down, then exit the door ahead and drop back down onto the topside landing bay to end the level.