A team of drug dealers kidnaps a busload of school children in order to get Five-0 to return the drugs they confiscated, while Joe White goes on a personal mission to uncover the identity of "Shelbourne" before Wo Fat does.

An autistic man helps Five-0 uncover the details of a daring bank heist, which ultimately leads to another showdown with Gabriel Waincroft. Meanwhile, Danny learns that the Feds want to talk to his mother about his brother's death.

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.

Five-0 captures a seriously wounded Gabriel Waincroft and prepare to bring him in, but Michelle Shioma wants him for herself to avenge the death of her father, and her men will stop at nothing to get him for themselves.

Five-0 must find McGarrett and Alicia when they are kidnapped by the serial killer they've been hunting.

When McGarrett gets a tip that someone is plotting a terrorist attack on Oahu, Five-O searches for those behind it before it's too late. Also, Chin and Abby have a very difficult decision to make.