Grace is still missing. Ethan heads to Chicago to investigate notorious attorney Marty Stein. DEA Agent Harper Deakins' investigation into one of Chicago's deadliest gangs takes a turn when a routine stakeout goes wrong.

In the fourth season, the show will move back to San Francisco as characters seek revenge and redemption. During his quest to slay his past ghosts, Ethan Kelly falls into a hellish labyrinth of criminality and betrayal by the police. Meanwhile, Mia Rochlan seeks revenge and will stop at nothing to make Ethan pay for double-crossing her.