Emily Byrne struggles to make sense of her time in captivity and her tumultuous past. Meanwhile, a deadly terrorist attack rocks the heart of Boston, drawing Special Agent Nick Durand and the FBI onto the case.

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.