Detective Steve McGarrett, a decorated Naval officer turned cop, returned to Oahu after Hawaii's former governor persuaded him to head up the new team: his rules, no red tape and full blanket authority to hunt down the biggest "game" in town. Joining McGarrett are Detective Danny "Danno" Williams, a relocated ex-New Jersey cop who is committed to keeping the islands safe for his children; Captain Lou Grover, who formerly headed Hawaii's SWAT unit; Jerry Ortega, the islands' local conspiracy theorist; and Tani Rey, a bold, recent police academy graduate.
Helping them is Adam Noshimuri, a friend with old ties to a deadly crime family; Junior Reigns, a former SEAL who comes to McGarrett looking for a job; Kamekona, a local entrepreneur who has his pulse on the Island; Sgt. Duke Lukela, a trusted member of the HPD; and medical examiner Dr. Noelani Cunha. The state's brash Five-0 unit, who may spar and jest among themselves, remain determined to eliminate the seedy elements from the 50th state.
(Do Not Disturb the Water That Is Tranquil) A murder leads Five-0 to investigate a centuries-old pirate story involving buried treasure, and it seems that the killer is using the back of a stolen painting as a treasure map. Also, the morning after their wedding, Kono and Adam (Ian Anthony Dale) are kidnapped and tortured by Gabriel (Christopher Sean), and Danny shows concern for McGarrett regarding Catherine’s return to the island.
(Ashes to Ashes) Five-0 investigates when a bomb squad is attacked and the culprit threatens to detonate additional hidden explosive devices unless arsonist Jason Sinclair is released from prison. Also, after Adam returns from the hospital, Kono realizes that they are being watched, and McGarrett prepares to take his relationship with Catherine to the next level.
(The Chilling Storm Is on the Mountains) While Five-0 investigates a scuba diver’s death from a gun recently used in another murder, McGarrett prepares to propose to Catherine.
(Best Laid Plans) Five-0 investigates when a wealthy recluse is found dead in a remote field with nearly one million dollars in counterfeit bills. Also, Adam is kidnapped by the Yakuza and forced to torture one of Gabriel’s men.
(Big Lie) Five-0 must interrogate members of a stunt bikers gang to find a killer who escaped by jumping his motorcycle from one roof onto another. Also, the team prepares to race in a Tough Mudder competition.
(Monsters) It’s Halloween in O’ahu, and Five-0 must track down a serial killer inspired by Frankenstein. Also, Jerry calls Five-0 for help when an armed gang raids a blood bank, and Danny must track down Grace who lied and snuck out to a Halloween party.
(Day Trippers) McGarrett’s first date with Lynn (Sarah Carter) on a deserted island turns deadly when a mob boss hiding there hunts them down in order to keep his location a secret. Also, Chin, Kono and Grover must race against the game clock to locate the father of a high school football star who will be murdered by a local gambler if his son doesn’t throw the big game.
(The Artful Dodger) Five-0 must work with charming con man Hank Weber to find a killer when his female partner is murdered on the job. Also, San Francisco Police Inspector Abby Dunn comes to O’ahu and works with Chin to investigate the murders of five Chinese arms dealers.
(Charade) Five-0 goes back to school when a college professor is killed and Danny goes undercover as his replacement.
(The Sweet Science) The brother of a promising local boxer is murdered, and the chief suspect is the outspoken reigning champion opponent from the mainland.
(One's Personal Sense of Responsibility) While McGarrett and Danny attend a couples retreat in Maui to work on their partnership issues, Kamekona’s dangerous past comes back to haunt him.
(Love Gives Life Within) Aunt Deb returns to Hawaii to scatter her husband Leonard's ashes. She enlists McGarrett, Mary, and Joanie for help with a bucket list she and her departed husband intended to do together.
(Hold The Breath) While Grover travels to Chicago to finally get a confession from Clay Maxwell about killing his wife, Chin and Kono are held at gunpoint by two killers who have no idea they are cops.
(Misery Loves Company) As Five-0 investigates a double homicide involving marital infidelity, McGarrett and the team recount their disastrous Valentine’s Day experiences.
(The Good Soldier) While Danny’s mother is questioned by the FBI, McGarrett partners with a young man with autism who may have information to help solve the murder of his only friend.
(The Solid Cornerstone) When Five-0’s sketchy confidential informant is accused of murder, McGarrett asks his old friend Odell Martin to defend him.
(Assets) McGarrett and Five-0 must track down a Russian spy who has stolen a flash drive containing classified NSA information that puts the life of a member of their Ohana at risk. Also, McGarrett finally learns why Catherine left him, and Abby continues to conceal her actual mission from Chin and Five-0.
(The Hunter) When a man is found left for dead drifting off the coast of Oahu, Five-0 uncovers a deadly slave trade operating aboard an illegal fishing vessel. Also, while Danny is out with his children, his car is stolen so he commandeers a bus to chase down the thieves.
(Care For One's People) A case from 25 years ago forces Grover to take his family on the run when a dangerous mob boss tracks him down to seek revenge.
(Rampage) While Five-0 investigates the theft of a high tech, indestructible suit built for the U.S. military, Jerry helps his sister try to save a captive elephant.
(The Cost of Freedom) Five-0 goes on a manhunt when a deliberate chemical spill enables six dangerous inmates to escape, including Kono’s husband, Adam.
(For the World to Know) Five-0 tries to save a kidnapped college student from a dangerous vigilante. Meanwhile, Max, Kamekona and Flippa fight to survive after being shipwrecked.
(Blood Ties) When a woman is murdered in her home, Five-0 learns that one of their own has a deep connection to the victim’s young daughter.
(The Entrance Is Stopped with a Spider's Web) Trapped inside a dilapidated building in Oahu’s Chinatown, Five-0 must protect a wounded Gabriel and plan their escape when enemy gunmen storm the building looking to kill him and anyone who gets in their way.
(My Desire Is Only for the Chief) In order to stop a meth epidemic on the Island, McGarrett and Danny go undercover as drug pilots, but when McGarrett is seriously wounded, Danny is forced to break their cover and land the plane in order to save his partner’s life.