Gus was screening and searching the passengers who were assembled at Norton Airfield. In the shelter where he worked, Kate Warner spotted her sister Marie after the nuclear weapon retrieved from Omar was found to be fake. She went to pursue Marie, but Gus, who assumed that Kate was one of the passengers, stopped her. Kate showed Gus her CTU identification tag, so he let her through.
As Kate left, she asked Gus to contact Jack Bauer, and he did so. Jack showed up with a group of agents and stopped Marie before she could kill Kate.