Walk to Pitne For and find out what's going on. You can use a renegade interrupt to threaten him if you want. He'll explain the dirty shipment that he's a part of and he should give you the passcode. He apparently decided to trick the Eclipse Sisters, which is why his partner is dead. You can take the elevator near him up to the Eclipse Hideout. Go on up. There's a mech right next to the door. Just take it down and get behind some cover. Hold your position and watch for the Eclipse mercs up ahead. You should be able to shoot right through their little guard post. I assume you're pretty good with combat by this point in the game. Regardless, clear the room and grab the new Scimitar Shotgun from the table.
As a side note, we'll be introduced to the special toxin. These red clouds will give a boost to biotics, but the toxin will build quickly. It will start to hurt you if the meter fills, so get ready to run to a new spot if you get caught in a cloud. You can also shoot the canisters of toxin around the Eclipse Sisters to kill them, just like an explosive barrel.
You can check a side room to find a girl named Elnora. She claims to want out. You can be nice and ignore the renegade interrupt, or you can gun her down for some renegade points. The paragon path will give you some information on the ship. Note that she is actually a heartless murderer, as you'll learn later on, so it is a little more justifiable. Grab some biotics research in back and then move out. Go up the stairs and engage another group. There's nothing too exciting.
Keep moving and keep up the fight. You'll find more mechs and more sisters. You'll basically have the same battle a few more times and then come out to a much more open area with a gunship visible in the background. It should just fly off. Don't bother damaging it now. It will repair before we see it again.
Move on over to the next group of mechs and take them out. Cross the little bridge and you should see a gunship pull right up.
