While Five-0 races to stop a mad bomber before he kills again, Danny gets an unexpected visit from his little brother, Matt, a fun-loving, Wall Street broker. The family reunion is cut short, however, when Danny discovers the real reason that Matt is in Hawaii.

When the team almost causes an international incident, Lt. Gov. Denning decides that one of them should be fired; Chin Ho faces the harrowing task of choosing a Valentine's Day gift for Malia.

An Aloha Girls camping trip with Grace turns deadly when an armed man takes McGarrett and a little girl hostage. Meanwhile, Adam introduces Kono to his dangerous brother who was recently released from prison.