Following McGarrett and Wo Fat's escape, gunmen hit Five-0 headquarters; McGarrett must turn on his own in order to find Catherine.
O'ahu goes on lockdown as the team look for a terrorist who is using weaponised drones on civilians; McGarrett and Danno attend a review with a psychologist.
When a man from Detroit is killed on the streets of Oahu, the team are shocked to discover the killer's motives; Chin risks everything to help Danny.
Five-0 need the help of American football star Arian Foster to solve the murder of an executive whose drink was spiked.
Christmas proves far from merry for the Five-0 when they make their way to the Big Island to solve a cowboy's murder.