An insurance investigator (Kristin Lehman) assists Castle and Beckett with a homicide case stemming from the theft of a costly sculpture, and a museum benefactor (Jessica Tuck) becomes one of the murder suspects.
Castle, Esposito and Ryan head to Atlantic City to solve the murder of a New Jersey casino owner who was found in an abandoned New York City warehouse. While there, they have a bachelor party for Ryan.
A sniper goes on a murder rampage in the city, and police struggle to find a motive before time runs out and another victim is killed. Meanwhile, Beckett's PTSD symptoms escalate, but she attempts to hide them from the team.
Castle and Beckett are abducted and awaken in a locked room, handcuffed to one another in a bed. As their coworkers search for them, they struggle to remember what happened and attempt to mount an escape.