Catherine “Cat” Chandler is a homicide detective who is haunted by her past. Years ago, she witnessed her mother's murder and was almost killed herself before being saved by a creature. A recent murder case leads her to Vincent Keller, a scientist assumed dead, who is in fact her savior. Part of an experimental military program, Keller's senses were heightened. But there is a terrible side effect - he loses control of himself when his adrenaline kicks in. The government ordered all members of the program to be killed, but Keller escaped and is now in hiding. Keller reveals that Cat's mother was being followed by the FBI and now Cat is also embroiled in this mystery.