Traynor will have discovered a Cerberus base that is giving the enemy the leg up in the region. You will be tasked with flying there are destroying the Cerberus presence, taking the base over for the Alliance. You will begin this mission on a landing pad, near one of the Cerberus ships. Either use the ship for cover to pick off enemies from a distance, or move in close with a Shotgun or Assault Rifle and take cover by the crates lining the walls.
This mission basically requires you to sweep through the entire base and destroy any enemy presence along the way. There are several key points where the enemies will like to gather up. First, head down the ramp to the lower level of the offices. You will find a Combat Engineer and a turret or two down here, most likely, as they have had plenty of time to set up at this point. You can easily flank around the enemies inside of the office by commanding your squad-mates to take cover on the thin entryways to the front door before looping around to the side of the building and entering through the side door. Be prepared for very close-quarters combat if you use this strategy. Nova works wonders inside this confined area, as do Grenades. Search this area from credits and a Pistol Magazine Upgrade Mod, and examine the panel on the wall to get the Heating Unit Schematics before heading out to the next area.
Head to the upper levels if you have yet to clear out the base. A ladder to the side of the small room you were just in will lead you here. You may find the remaining Assault Troopers huddled up here. Once all of the enemies are dead, follow the waypoint to the panel. You will have to hack the panel to disable the Anti-Air weapons protecting the base. Assign EDI or Liara to do the job if you have them in your party, as you will get the fastest results from a more brainy squad-mate. Take the stronger of your squad-mates, James or Garrus, and defend the base. Assign your squad-mate to hold down the room from the right-hand entrance, while you exit through the front and mop up the enemies in an arc, eventually meeting up with your squad-mate back at the side entrance.
You will have to take down one final wave of troops, including Nemesis snipers and an Atlas mech, after the panel has been hacked. As usual, you can either focus brute force on the Atlas or hijack it for yourself. As for the other enemies, handle most of them as normal and be sure not to let the Nemesis snipers out of your sight. They are fast, and can easily flank you. When all of the enemies are dead, the Alliance will take the base over and you will be whisked back to the Normandy.