After fighting off an assassin in his own home, McGarrett and Joe White flee to Montana to prepare for a battle against those exacting revenge for a past SEAL mission.

Steve and Catherine are still reeling from the murder of one of their ohana and, along with Danny, Junior and some old friends, Harry Langford and Wade Gutches, hunt down the killer. Also, Tani and Grover investigate when a bag of human bones, discovered inside an abandoned storage locker, goes missing.