Longworth teams up with his old partner, Detective Samantha Harper to track a serial killer from Chicago and Callie can't help but notice the obvious chemistry between them. Manus asks Callie to work as a forensic nurse for the FDLE.

A beautiful synchronized swimmer in an elaborate mermaid costume washes ashore dead, and the clues lead Jim to a bittersweet love triangle and a hip hop mogul trying to turn a mermaid show into multimillion-dollar phenomenon. On the home front, Callie hits a wall in her job search, and Jim realizes the best opportunity for her is the one in Atlanta she passed up to be with him.

Longworth and Jennifer investigate a murder that puts them at odds with the Sovereign Citizens, a bizarre anti-government group that believes they are above the law. Manus and Carlos soon find themselves victims of the Sovereigns' paper terrorism attacks when they are suspended from duty. Callie desperately searches for her old cell phone where she recorded Elkins blackmailing her into sleeping with him for overlooking her tax issues.