A bomb goes off in an office building. After Higgins and Maleah race up Diamond Head, Juliet spots the smoke from the explosion, which killed three. Duke tells Katsumoto that the device was a small fertilizer bomb. The bomber wearing a hoodie is caught on surveillance. Rick suggests that La Mariana supply first responders with food and water. Nora Simmons arrives at the gate looking for Thomas and Juliet. Nora fears her son Ryder is the bomber. She says Ryder has been angry since his father died last year. Nora wants them to find Ryder and turn him in safely to the police. At the explosion site, T.C. hides when he sees firefighter Mahina. T.C. was worried because he hadn't called her back after their date. But she didn't even remember him. The police, including Gordon, show up in force at Nora's home. T.C. unsuccessfully tries to spark Mahina's memory and apologizes for not calling. Magnum and Higgins check out the former Simmons family boat and find Ryder there. Ryder pulled the fire alarm and says he didn't have a choice but to plant the bomb. They turn him in to Katsumoto. Ryder confesses and says he acted alone. After interrogation, Gordon knows Ryder is lying about that. Thomas and Juliet investigate Ryder's movements before the bombing. They find a nursery, which would use fertilizer, on Ryder's route. Magnum breaks into a locked shed and finds bomb-making components inside. The nursery is owned by the Simmons' neighbor Pete. They find a set of blueprints for another building. The second building is where the government stores money set to be retired. The power got shut off to that grid and the heist is underway. The thieves get trapped in the vault. Pete had threatened Nora. Mahina gives T.C. a second chance.