The island of O'ahu goes on lockdown when Five-0 hunts a terrorist who starts using weaponized drones on civilians. Meanwhile, McGarrett and Danno must go for a mandated review with a psychologist, resulting in a session which looks a lot like couples therapy.
Five-0 investigates when the young daughter of a Navy Seal currently on a top-secret mission is kidnapped. Meanwhile, with his brother's life on the line, Danny must locate the $18.5 million he owes his captors.
Five-0 investigates when three female thieves unknowingly steal something during a tour bus robbery that makes them a serious target. Meanwhile, Danny searches for his brother's hidden millions in order to exchange it for his life.
When a Detroit hit man is taken out by one of his colleagues on the streets of Oahu, Five-0 is shocked to learn the killer's surprising motives. Meanwhile, Chin puts his career on the line to help Danny get the money he needs to save his bother's life.
On the fourth anniversary of his father's death, McGarrett meets a woman who helps him reopen the last unsolved case his father worked on before his death.
It's Halloween and Five-0 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.
When McGarrett is kidnapped by Wo Fat, he experiences what would have happened to the team if they had taken a very different path.
While the team investigates a couple's murder in which their sons are the prime suspects, McGarrett is shocked when Aunt Deb returns to the island with her new fiancé.
It's Christmas in Hawaii and Five-0 travels to the Big Island, where Max is forced to work with a rival medical examiner after a cowboy is poisoned. Meanwhile, McGarrett pressures Danny into stealing a Christmas tree.
Five-0 enlists the help of an old-school private detective to solve the murder of a young woman who was secretly working as an escort.
When a tourist is killed after unknowingly transporting a stolen Van Gogh, an undercover Kono and Chin enter the world of black market priceless art and are taken hostage. Also, McGarrett asks Iron Chef Masaharu Morimoto to help train Kamekona to beat Chef Sam Choy in a shrimp cook-off.
When a neurosurgeon is assassinated just before performing surgery, Five-0 uncovers the shocking truth behind the disappearance of four reform school boys 40 years ago. Also, McGarrett's Mercury Marquis is stolen by an unlikely culprit.
A patient infected with a contagious and lethal strain of bird flu is kidnapped and the culprits intend to weaponize the virus.
While Five-0 hunts for a notorious criminal who has never been seen, Kono must fight for her life when she discovers the villain's identity. Also, Kono confesses to Adam that she's conflicted about their future together because of his ties to his formerly corrupt family business.
When a journalist is killed, Five-0 must use his past reporting to hunt down a presumed dead Congolese warlord who is alive and well living on Oahu. Also, as Valentine's Day approaches, Danny overreacts when Grace's texts to a boy start accidently coming up on his cell phone.
A California ATF agent helps Five-0 hunt a serial arsonist who is targeting couples on Oahu. Meanwhile, Danny takes Amber on a romantic getaway, but her abusive ex-husband tracks them down with the intent of taking Amber back.
McGarrett and Danny work on their relationship while they stakeout a woman's apartment after she escapes following a diamond robbery.
McGarrett enlists Joe's help after Danny and Chin are arrested for deadly past transgressions.
McGarrett and Odell come under siege in Odell's barbershop when they try to protect a young man who is being hunted down by a gang. Also, Jerry is wrongfully accused of committing a series of home invasions.
When Grover's oldest and closest friend tells him he witnessed his wife fall off a cliff to her death, Grover's gut instinct tells him that this was no accident. Also, Danny and Dr. Shaw get trapped in an elevator with a dead body in need of processing.
When a performer is killed at a convention of Elvis impersonators and his body is stolen, Five-0 must track down the culprits who are after the hidden diamonds sewn into the victim's costume. Also, Gabriel Waincroft returns to ask for Chin for help getting off the island.
When a woman is found murdered in the hotel suite occupied by three married men, Five-0 must help the friends get over their massive hangover and retrace their steps from a wild night to find the killer. Also, Jerry witnesses a woman's kidnapping on the streets of O'ahu.
When Kono goes on a solo outrigger trip around the Hawaiian islands in honor of her mother, she hits a patch of wild weather and must fight to stay alive. As Five-0 searches for Kono, they investigate a man busted for cooking meth who claims he received a threat on his son's life if he didn't continue making the drug.
Five-0 investigates the murder of a bounty hunter who was killed after he apprehended a fugitive. Meanwhile, Rachel reveals a long-held secret to Danny that has serious ramifications.
Season 5 ends with Five-0 learning that a stolen nuclear bomb is somewhere on the island and is about to be detonated. Meanwhile, McGarrett is stunned when Catherine returns to Hawaii; and Chin confronts Adam about his lingering connections to the Yakuza, on the eve of Adam and Kono's wedding.