Spoilers for this episode.
Jack tracks Henderson to his house after surviving the bunker explosion. Miriam Henderson is shocked to see him alive and rejects his accusations against her husband. Jack uses the home computer to search for communications while waiting for Christopher to return. At CTU, evidence recovered after the motorcade attack points to a ventilation system at Tyler Memorial Hospital. Curtis heads there as staff struggle to move patients who cannot simply walk out.
A terrorist disguised as an orderly reaches the hospital's ventilation area with a gas canister. Curtis kills him, but the device is already armed and the chemical response team cannot disarm it before the timer expires. Curtis carries it out of the building to a containment unit. The canister opens after it has been sealed inside, sparing the patients still waiting for evacuation and preventing another release into a crowded public building.
Henderson returns home and Jack captures him. When threats against Christopher fail, Jack shoots Miriam in the leg to pressure him into answering. Henderson still refuses, and Jack calls for medical help and a harsher interrogation at CTU. McGill meanwhile tries to retrieve the access card stolen by his sister. Before it can be returned, Ostroff kills Jenny and her boyfriend, takes the card and prepares to use it to enter CTU itself.