While McGarrett sits in prison awaiting trial for the murder of the governor, Danny brings him a surprise visitor to help clear him. Meanwhile, Kono is suspended from the force, pending an internal investigation.

Steve goes to Cat for help finding his mother. When an art heist turns deadly, Five-0 turns to August March.

When threats turn deadly against a tour company that endangers the local shark population, Five-0 faces the difficult task of narrowing down the suspect list. Meanwhile, the team debates whether or not Kamekona will earn his helicopter license.

When Halloween comes to Hawaii and a zombie-like man is shot, Five-0 races to stop a madman who is conducting experiments on humans.

McGarrett and Odell come under siege in Odell's barbershop when they try to protect a young man who is being hunted down by a gang. Also, Jerry is wrongfully accused of committing a series of home invasions.

Five-0 must interrogate members of a stunt bikers gang to find a killer who escaped by jumping his motorcycle from one roof onto another. Also, the team prepares to race in a Tough Mudder competition.