McGarrett interrupts high-tech thieves who disabled his elaborate security system and let themselves in; he's outmanned and they end up stealing his father's Champ box. Realizing they had to have had a key, McGarrett and Danny race to his sister Mary's house, only to find evidence she's been kidnapped. McGarrett and Danny manage to rescue Mary and confirm that the Yakuza (Japanese mafia) were behind the kidnapping and the theft and both are connected to the murder of McGarrett's mother. Mary's investigations have instigated the recent attacks on the McGarrett family and she tells her brother that their father was working on two investigations, she's not sure about one, but the other is the murder of their mother. McGarrett believes the bomb that killed his mother, was intended for his father, and meant to stop his investigation into the Yakuza 15 years ago. He and the team pick up the trail and identify a very wealthy and well-connected businessman as the Yakuza boss. He's so well connected, he eats lunch with the Governor; she, in turn, tells McGarrett to tread carefully. Our teams solves the case of McGarrett's mother's murder and brings down the Yakuza boss, but not without annoying the Governor and, perhaps, agitating Wo Fat.