Spoilers for this episode.
With Rossler dead, Jack takes his place in the planned delivery of the trigger chip. The terrorists collect him and bring a nerve-gas canister along to test it. CTU follows, expecting to recover the weapon, until the route leads to a shopping mall. Jack is forced inside with the men as they pose as air-conditioning workers. Their destination is the ventilation system, where one canister could poison shoppers throughout the building.
McGill argues that allowing the attack will preserve their chance to find the other nineteen canisters. Buchanan supports the calculation, Audrey objects, and Logan authorizes the release. Listening to the decision, Jack refuses to provide a working activation code. The terrorists knock him unconscious and switch to opening the canister manually. Jack wakes, overpowers the man sent to kill him and stops the flow, but some gas has already entered the ducts.
Jack shuts down ventilation and helps evacuate the mall, carrying an injured girl outside and getting her treatment. Polakov escapes with the chip, allowing Chloe to track him to the terrorists' workshop. Erwich realizes he has been followed and leaves with the other canisters; Polakov kills himself as CTU enters. At the retreat, Martha finds that the planned statement conceals Cummings' involvement. Faced with his grieving widow, she cannot bring herself to explain what he did.