A murder mystery sends Five-0 in search of pirate treasure. Meanwhile, Gabriel Waincroft holds Kono and Adam hostage after their wedding and demands the money they were using to pay off the Yakuza.

Five-0 interrogates members of a stunt biker gang to locate a killer who escaped by jumping his motorcycle from one rooftop to another. Meanwhile, the riders prepare to race in a Tough Mudder competition.

The team investigates a bizarre killing at a hospital. Just as a team was going to operate on a man who was brought in, someone posing as doctor killed everyone including the patient. Max tells Steve that the killer also cut the patient. Steve thinks the man had something in him. They locate the doctor who did the procedure who says he placed a flash-drive in the man. The doctor says another guy paid him to do that. They learn he's computer programmer, who works for a company that works for the NSA. His superiors inform Steve that they fear there may have been a breach and the programmer is the one who did it. Steve tries to question him but he escapes. They learn the killer is the programmer's girlfriend and that she's a Russian spy. They find them but she starts shooting and gets away. Steve talks to the programmer who says he thought he was doing something noble but it turns out he was duped by the girl. Steve is then informed that among the info he downloaded has info on someone he knows who is on a undercover assignment. The programmer says the info is safe because he encrypted it. But that's when everyone passes out, when they wake up they find the programmer gone. Evidently she took him to open the file. So they have to find him before he does. Steve also tells everyone who is behind the investigation on them.

While investigating Flippa's friend's murder, McGarrett and Grover uncover a deadly plan by an extremist group on the island. Also, Grover has an emotional reaction to the case.