Properties belonging to Yuhio Muromoto (Bennett Ohta) are bombed by Willy Barker (David Dukes), a student in his daughter Nancy's (Donna Benz) photography class. Only Ohta's confidential secretary, Alicia (Anne Francis), knows about the phone threats he's been receiving.
McGarrett concludes that the bombings are personally motivated and begins checking up on Muromoto's life before he came to the Islands. A visit with the Japanese consul, Mr. Sakata (Tom Fujiwara), yields nothing. However, Steve's belief is reinforced when lab findings reveal that the third blast was set off by a WW 11 hand grenade and a fourth by a land mine.
Chin Ho's investigation of the source of the explosives reveals that they were sold to a Charlie Mitchell in Honolulu. When the Five-0 team arrives at his apartment, they learn that he has recently died and the room taken over by a Willy Barker. Danny remembers meeting Barker who was with Nancy at the last blast site.
Meanwhile, Willy has lured Nancy into a photographic field trip. When they arrive at Mitchell's cane field compound, Willy ties her up and calls Muromoto. He says it's too late for Muromoto to confess his sins in public, now he must do as ordered or his daughter will die. Muromoto agrees.
Only minutes after Muromoto has left in his car, McGarrett arrives. When he learns of the phone call and Nancy's field trip with Willy, he calls out the HPD choppers to look for Muromoto's car. The car is soon spotted, and McGarrett and Danny are given direction from the air.
Muromoto arrives at the compound and is himself tied up. Willy claims that Muromoto was the commander of a death camp on Bataan and that he executed Willy's father. Charlie Mitchell saw it happen. Nancy wants to know how he can prove it after so many years. Simple. Muromoto told everything to his trusted secretary, Alicia, when they were lovers. Now she wants revenge because he failed to marry her after his wife died.
Alicia orders the programmed Willy to kill Muromoto but he drifts into a catatonic state. As Alicia tries to tongue-lash him into action, McGarrett and Danny arrive to arrest the pair. A reporter (Joshua Bryant), who had trailed McGarrett to the site, asks whether his story should be about World War II. Steve says, "The real story is about people who won't let go of hate, and what it does to them and others."
NOTE: Tom Fujiwara looked very official with a conservative suit and slicked down hair, but he couldn't suppress that sweet smile of his at the end of the scene.