As a U.S. Deputy Marshal, based on Miami, Florida's Gold Coast, Karen must deal with the underbelly of South Beach nightlife and Palm Beach high life while tracking down fugitives. She also struggles to win the respect of her fellow officers. Karen occasionally gets advice from her father, a retired Miami police officer turned private investigator, who is Karen’s confidant, counselor, and confessor.

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.

Stranded outside her silo with a failing suit, Juliette Nichols races against time, stunned to find another silo nearby that could be her only hope for survival. Meanwhile, unrest brews inside her original silo as Bernard Holland rallies citizens to maintain order amid rising questions about their world. As Juliette faces unexpected dangers near the new silo, hidden truths about the silos’ origins and the world beyond begin to surface, deepening the mystery.