When Kono goes on a solo outrigger trip around the Hawaiian islands in honor of her mother, she hits a patch of wild weather and must fight to stay alive. As Five-0 searches for Kono, they investigate a man busted for cooking meth who claims he received a threat on his son's life if he didn't continue making the drug.

Season 5 ends with Five-0 learning that a stolen nuclear bomb is somewhere on the island and is about to be detonated. Meanwhile, McGarrett is stunned when Catherine returns to Hawaii; and Chin confronts Adam about his lingering connections to the Yakuza, on the eve of Adam and Kono's wedding.