Five-0 is called in when Zack Slater, a gifted computer hacker, is kidnapped by masked thugs as his parents drive him home from his six month stint in prison. Chin Ho and Kono canvas the scene of the kidnapping and question Zack's family, including his autistic little brother, James, who winded up memorizing the license plate of the kidnapper's vehicle. Five-0 tracks the vehicle to HPD impound, where they discover Zack's dead body in the trunk. After examining the body, Max tells them that Zack died from a heart attack brought on by torture, and that the kidnappers ended up performing CPR to save him. McGarrett concludes that whoever took Zack wanted information from him, but failed to get it. Initially, evidence points to Kong Li, a notorious cyber-criminal who visited Zack in prison. Danny enlists Adam 'Toast' Charles (EP #102) to get to Kong Li, but Li had nothing to do with the kidnapping. Chin Ho and Kono discover that Zack uploaded a secure file to a file-sharing site before he was sent to prison, so Kono goes to speak with Zack's family, where she eventually discovers that Zack taught the password to his younger brother, James. Before she can relay this to the team, a trained team led by ex-Special Forces baddie Sean Winston storms the house and holds all the guests as hostages. Zack hacked the mainframe to Winston's Blackwater-esque group and uncovered a villainous mobster that Winston had helped disappear, ala Whitey Bulger, so he needed to get the file back to cover his tracks. After a tense standoff and exciting chase, Five-0 subdues Winston and his team and arrests the fugitive mobster.
Meanwhile, McGarrett tries to stage a reunion between his mother, Doris, and his sister, Mary, but Mary can't bring herself to go through with it. Mary comes to Hawaii with Morty Sapperstein, a mouthy geriatric who she now takes care of full time, and it is Morty who winds up convincing her to go see her mother before it's too late.