When Captain Grover's friend disappears, Five-0 discovers that his friend was hiding a dangerous secret. Meanwhile, Danny befriends a New Yorker new to the island, and Kono reunites with Adam.
Five-0 investigates the murder of a real estate agent, Danny's mother comes to Hawaii with big surprise news, and captain Grover reveals a secret about his past to McGarrett.
Five-0 looks for a 16-year-old girl who is kidnapped after her father is murdered, Danny launches a plan to keep his mother from getting a divorce, and Jerry uncovers a new clue for McGarrett related to "Shelbourne."
One of Chin Ho and Jerry's high school classmates is killed during their class reunion, and McGarrett and Danny find a new clue at the secret burial site.
While Five-0 investigates a homicide related to a stolen transplant organ, McGarrett joins Catherine for a trip to Afghanistan so she can help a friend whose son has been kidnapped by the Taliban.
Cyber-criminal Ian Wright holds Grover's daughter hostage and demands that Grover help him out with a multi-million dollar heist. Meanwhile, Wo Fat escapes from maximum security in Colorado.
The young daughter of a Navy SEAL in Afghanistan is kidnapped, but Five-0 soon discovers that the kidnappers took the wrong girl and are negotiating with the wrong family.
Three surfers get more than they bargained for when they rob a tour bus, Jerry continues his investigation of a counterfeiter, and Danny searches for his brother's missing money.
Five-0 deals with a mob contract killer who has literally and figuratively had a change of heart. Danny finds his brother's money but is short five and a half million dollars, and his brother's life may be in the balance.
McGarrett meets an old acquaintance of his father's at his gravesite, which prompts him to investigate an old case his father was working on just before his death.
It's Halloween and Five-o must track down a serial killer who is copying murders depicted in a cult slasher film. Meanwhile, McGarrett must help Jerry after he is kidnapped by the counterfeiters he has been tracking.
Wo Fat kidnaps McGarrett to get answers about his father. He drugs McGarrett during his interrogation, which causes him to have hallucinations that his father is still alive.
A man who conned people with bad investments is murdered along with his wife, and their children are suspects. Meanwhile, McGarrett's Aunt Deb returns to Hawaii with surprise news.