Head up the stairs. Pick up the audio diary (What's Happening Here) that is on top of some rubble near the Circus of Values machine. Moving on, travel down the street. A Big Daddy and Little Sister can be found in this area. Kill the Big Daddy, then either rescue or harvest the Little Sister. Move through the archway at the very end of the street.
There are several vending stations in this area, including a Gatherer's Garden. Look to the ground and pick up the audio diary (Atlas Lives) on the floor by the Gatherer's Garden machine. Use the U-Invent station to create some ammunition, if you have the materials. Grenade Launcher ammo especially would be of great help, to deal with Turrets and such since you no longer have a choice over which plasmid you can use.
The Second Dose
Travel down the street leading to the Artemis Suites. There is a turret and Security Camera along the street, they may give you some trouble, since you presently do not have a choice over which plasmid you are able to use. Destroy the Security Camera on the wall on the opposite side of the room. Take the stairs up to the second floor walkway, walk along until you find Dr. Suchong's clinic. There is a Security Camera on the wall to the left of the door, have a weapon ready and peek around the corner, destroy it quickly to avoid setting off the alarms. A turret sits around the corner, too.
Enter the bathroom on the right, pick up the Medical Expert 3 tonic which is on the ground in the third stall. Leave the bathroom and Suchlong's office, the door being in the area right across from the bathroom's door. Pick up the audio diary (Protections Bond) on the floor, then walk over to the table and take the second dose of the Lot 192 formula.
Before you leave, be sure that you have dealt with two Little Sisters in this level. There is only one Big Daddy location in this level, and that is the area that you encountered the first one. By now, a new Big Daddy should have taken the dead one's place.
Leave the Artemis Suites and take the street down to Fontaine's Center for the Poor. Enter the Center, turn right and look in the Steamer Trunk for an audio diary (Meeting Atlas). The last Big Daddy occupies the foyer. Be sure that he has a Little Sister with him, then kill him. If you have rescued all of the Little Sisters that you have encountered up to now, after rescuing this one, Tenenbaum will send you another gift.
Take the stairs up to the fifth level. Enter Atlas' Headquarters. Careful, there is a Security Camera in this room. Take the stairs down to the lower floor. Take the audio diary (The Longest Con), and the Focused Hacker 2 tonic that are on the desk in this room. Search the bloody corpse on the broken desk and remove the audio diary (Today's Raid). On the wall far to the right of this corpse, there is a "Power To The People" Weapon Upgrade Station. You can raid Fontaine's gun stash here as well by using Telekinesis to pull the weapons to you.
To 4th Floor
To The Bathysphere
Outside of Fontaine's Home for the Poor, head down the ramp leading to the Rapture Metro. Take the elevator down to the Bathysphere station. Enter the Bathysphere and take it to the next level, Point Prometheus.