Charlie Crews and Dani Reese investigate the death of a family man who is found beaten and bound to a chair at the bottom of an empty pool. Captain Tidwell is convinced the murder was an act of gang violence and sends the detectives on assignment. After interviewing the victim's daughters and two gang members, Crews and Reese's only clues are an underground party circuit, a bottle of steroids, and a myth about a man only known as Monster. Meanwhile, Ted gets an unexpected visit from Dani's father who is determined to find out what information Crews has on him and consequently has a request of Ted. Crews also enlists the help of his ex-wife Jennifer to reach out to Rachel, the lone survivor of the murdered family Crews was wrongly convicted of killing.

A university's prison experiment goes horribly wrong when one of the students acting as a corrections officer ends up dead. Crews and Reese are in a race against the clock to find the killer. As they interview both prisoners and guards, the detectives discover the social experiment may have done more damage than good. Meanwhile, determined to figure out Jack Reese's connection to his case, Crews obsesses over a recording he obtained from a wiretap he placed on Reese.