McGarrett crosses the line and is arrested while investigating the death of his former SEAL buddy, who died while making an emergency landing on an aircraft carrier, and the only survivor is a baby. Also, Adam returns to Oahu with some devastating news about his marriage.

After fighting off an assassin in his own home, McGarrett and Joe White flee to Montana to prepare for a battle against those exacting revenge for a past SEAL mission.

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.

Five-0 must locate a teen girl who purchased a gun from a junkie, and discover that the firearm, over the course of decades, has affected all of their lives.

Fugitive hacker Aaron Wright resurfaces to ask Five-0 for help when his co-workers at the NSA, which he has been working for, are all murdered. Also, Junior speaks at the parole hearing of the drunk driver who killed his sister.

It's Thanksgiving, and while Junior and Tani track down the thief who robbed his parents' home, Five-0 investigates the murder of a beloved philanthropist and the theft of his ultra-valuable koa tree. Also, Danny moves in with McGarrett.

When Adam's girlfriend, Tamiko, is kidnapped right in front of him, he shuts out Five-0 and breaks all the rules in order to get her back. Also, Five-0 investigates three seemingly unconnected homicides.

Harry Langford helps Five-0 investigate a series of murders that follow the plot of a fabled unpublished crime novel from the 1920s. Also, Tani and Junior's friendship takes a meaningful new turn.