Season 4 focuses on a research team recruited by Homeland Security agent Don Self to obtain Scylla. Although the team initially believes it is in the Companion's Black List, the team is later released to gather information on an advanced renewable battery. In the first half of season 4, the team attempts to obtain an access card to Scylla, and break into the Companion headquarters to steal it. Sara is discovered to be alive, while Bellick is killed. Agent Don Self is revealed to be a double agent and is planning to sell Scylla to the highest bidder.