After the murder of a judge's child, the Five-0 team begins investigating a bomber with a potential grudge against the judge and legal system. A second blast kills a prosecting attorney's, Yoon, son. Chin Ho takes a fragment of the circuit board from the second bombing to a hobby shop and is informed that somebody came in and bought three of them. Kono and Chin Ho cross-reference the information and discover a suspect, Marshall Roan, who's son was recently killed in prison. They eventually uncover the final target and stop Roan before he's able to kill anybody else.
Danny learns that his visiting brother, Chris, is the target of a federal investigation. Chris came to Hawaii for one last deal. Danny lets his brother go rather than arresting him and sending him to jail.