After a description of the Inner Circle, Mona has you look for Corcoran. She will give instructions for the first half of the level.
She first give a direct route to the apartment to attack two cleaners. You can follow her path, but for a short-range attack, you can go forward, make a left turn and attack the cleaners. The door will close and lock, requiring you to use the apartment to the right - there are two cleaners to the right of the entrance.
Exit to the balcony, and use it ro reach Corcoran's apartment. Head to the upper floor, where there are two cleaners in discussion, and additional cleaners in the back. Reach Corcoran, and you'll report to Mona that he is dead. You now need to escape, but you can't leave the way you came, because the cleaners took control of the elevator. But before leaving, take the four painkillers within the bathroom.
Take the exit to the 31st floor lobby, and follow the cleaners through the open apartment doors to the right. Head down the stairs, and take out the two cleaners at the piano, and the third jumping in from the window.
Exit to the balcony, and you can reach the 29th floor by a jump, after sniping the two cleaners on the balcony. The cleaners in the apartment will be alert and will attack as soon as the door opens, but you can throw a few grenades to soften them up. The only route is into the lobby, where a few cleaners gun down a single resident calling for help. Enter his apartment, look for painkillers in the bathroom, and head down the stairs again.
In the 28th floor lobby, one cleaner attacks from the right. Enter the apartment he was guarding, and approach the window. At this time, Mona will get attacked, requiring you to reach the lobby without guidance from her.
To the elevators
As Max said, he will use the window cleaner's elevator. You will head down only a small amount, before the elevator stops and the enemy throws grenades from the roof. Climb down, until you reach a wooden board, and enter by the window in the corner. You can retrieve two pain killers on the kitchen table. When ready, exit the room to the lobby.
The cleaners are already ready in the lobby, taking cover behind boxes. After these cleaners are taken care of, Kaufman will arrive with additioanl cleaners. Wipe them out, and look for an open elevator to reach the lobby.
After compleing this level, you will be arrested and brought to the police station. Any guns and painkillers you have will be removed.