A renowned urban vigilante is killed after making another citizen's arrest, and Five-0 delves into the world of super heroes and comic books to find the killer. Also, Adam finally gets closer to finding out who killed his sister.

Still reeling from the murder of one of their ohana, Steve and Catherine, along with Danny, Junior and some old friends, Harry Langford and Wade Gutches, hunt down the killer. Also, Tani and Grover investigate when a bag of human bones, discovered inside an abandoned storage locker goes missing.