Spoilers for this episode.
Jack and the surviving CTU staff shelter in sealed rooms after the nerve gas attack. Chloe can barely work while Edgar's body lies outside the window, and Kim's boyfriend Barry tries to help her focus. The gas contains a corrosive substance that is eating through the room seals. With rescue teams still too far away, the people inside must restart the ventilation system before their protected spaces are contaminated.
Jack holds his breath and enters the poisoned corridors, but a security grate blocks his route to the necessary computer. Lynn McGill can reach it from the holding room, although opening his door will also expose guard Harry Swinton. Lynn accepts the task, and Harry calls his daughter goodbye. Lynn disables the program and returns to the cell. Both men die as the ventilation begins clearing the building.
Kim refuses Jack's request to stay and talk once they can leave safely. Martha supports Logan while warning him against surrendering decisions to Gardner, and Homeland Security prepares to take over CTU. In medical, Tony again tries to kill Henderson for Michelle's murder. He hesitates over the syringe, allowing Henderson to seize it and stab him. Henderson escapes, and Tony appears to die in Jack's arms before help can save him.