While investigating Flippa’s friend’s murder, McGarrett and Grover uncover a deadly plan by an extremist group on the Island. Also, Grover has an emotional reaction to the case.

As a dangerous hurricane hits Oahu, Five-0 is tasked with protecting El Diablo, a captured serial killer who is being hunted by an assassin. Also, Tani's civilian safety check during the storm turns deadly and Rachel and Charlie evacuate to Danny's house, where the ex-spouses reminisce.

While Adam investigates the murder of an undercover FBI agent about to wed the daughter of a Yakuza leader, Noelani is held hostage and forced, along with her mentor Dr. Chu, to operate at gunpoint on a criminal.