The BAU is called to Oklahoma to investigate a murderous clown terrorizing the sleepy town of Guymon.
Halstead's past resurfaces when a former Army colleague is implicated. As the FBI launches an investigation into Roy's disappearance, Upton feels the pressure of the secret she and Voight are sharing.
Ducky is attacked by a man who claims to have information about his half-brother, who died decades earlier; Jake and Bishop talk about their future.