Emily Byrne struggles to make sense of her past, including her time held captive; Special Agent Nick Durand is sent to investigate a deadly terrorist attack in the heart of Boston.
Emily's investigation into her past becomes a hunt for a serial killer whose crimes have been overlooked in the citywide chaos. When the serial killer claims a victim close to Emily, she returns to the FBI to hunt him down, partnering with Special Agent Cal Isaac a former Navy SEAL with a personality that runs counter to Emily's.
Emily and Cal's investigation into the Fentanyl Killer points them toward some dangerous and highly skilled suspects. Elsewhere, Nick's manhunt for the Federal Annex attacker heats up.
While investigating the home of the most recent Fentanyl Killer victim, Emily obtains a critical piece of evidence. Meanwhile, Nick's work with a high-profile prisoner turns deadly.
Emily and Cal travel to Moldova to track down the Fentanyl Killer-a task that proves to be more dangerous than anticipated. Meanwhile, Nick is given an order that challenges his moral code.
After being declared dead in absentia, an FBI agent must reclaim her family, identity and innocence when she finds herself the prime suspect in a string of murders.
