A hard-as-nails Texas Ranger arrives on the island to look for his missing daughter, Kono and Adam's secure location is compromised, and an old friend comes to Catherine with a job offer.
A married couple's execution leads Five-0 to a mystery involving stolen artifacts and a long-forgotten secret society, and Catherine goes through her last day with the Navy.
McGarrett tries to find the man who killed his old SEAL friend Billy while he and Catherine were working a surveillance job, and he also turns to Joe White to track down his mother.
Five-0 tries to figure out who killed an officer who was working undercover for the ATF, while also babysitting for McGarrett's sister Mary's new baby.
A Secret-Servince agent's death leads Five-0 to believe that an assassin is targeting the President during his trip to Hawaii; McGarrett gets a surprise Thanksgiving visit from his Aunt Deb.
A murder attempt on a Pearl Harbor veteran leads Five-0 to use decades old evidence to investigate a deadly crime committed in an internment camp on Oahu during WWII.
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.