Season three reveals an origin story set centuries earlier, while continuing the saga of a dystopian society of 10,000 people living underground under mysterious circumstances. In the present, Juliette Nichols survives her forced "cleaning" but returns with memory loss as the silo recovers from rebellion and faces a dangerous new threat. Meanwhile, in the "Before Times," journalist Helen Drew and Congressman Daniel Keene uncover a conspiracy that pulls them into a chain of events with catastrophic, irreversible consequences.