Billy Ray Gallion

Members of the team go undercover at a university in order to track a hacker who is putting the world economy at risk. Walter conducts an experiment to prove that Ray's partner's death was not his fault.

McGarrett's mentor asks the team to look into the death of a Navy SEAL; Chin Ho is worried about Kono fraternising with some dirty cops.

The team take to the beautiful waters off Hawaii to investigate the murder of a deep sea diver known for his valuable shipwreck finds.

The team looks into the murder of a state's women's volleyball coach, and learn the bad news about Kono; Chin Ho tries to reconnect with Malia.

Wild beasts invade the survivors' beach encampment in the middle of the night; a secret is revealed about the mysterious Locke.

When Hayley finds herself being implicated in a cyber-terror attack after doing an old friend a favour, Castle and Beckett rush to clear her name.