Nash is out of action after Caitlin accidentally shoots him in the butt. Joe and Bettina do a joint investigation with FBI agents to bust a clever con-artist. Cassidy is stalked by a deranged college student.

Nash clashes with his new rival, Deputy Chief Max Pettit, who has assigned Cassidy to a dangerous undercover gig involving synthetic diamond smugglers and a deadly assassin working for the South African diamond cartel. Joe tries to back out of the house purchase; Cassidy and her new partner Rachel McCabe join the S.I.U.