After Steve's CIA agent friend is killed, McGarrett lets himself be captured by the group he thinks is responsible and endures a torturous sensory deprivation tank to find the hugger. Also, Tani wrestles with whether or not she will tell McGarrett about the hug weapon she found at Adam's house.
When a vacationing dad on a flight to Honolulu is kidnapped and force to parachute mid-flight, Danny, Tani and Junior track him through the jungle to discover that he may not be who he seems. Also, McGarrett is threatened with a secret from his past.
Crime spikes when a heat wave hits Oahu, causing McGarrett and Danny to hunt down a bank thief, and Tani and Junior's car is stolen while they're on duty. Also, Grover plays the golf game of a lifetime, and Kamekona incites a riot by price-gouging on his shave ice.
Jerry accompanies Junior as he escorts a fallen soldier home to Oahu. Also, McGarrett and Danny discover a dead body when they delve into the illegal and highly profitable black market for sand.
On Halloween, Jerry and his friends search his childhood camp for evidence to a hug he witnessed as a boy, while McGarrett investigates a little girl who drew pictures depicting the scene of a recent hug before it was discovered.
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.
McGarrett investigates a cold case from the 1940s, one that his grandfather and the famous Honolulu detective Chang Apana worked on, and he tries to deduce how the case could have been solved. Also, McGarrett and Danny get ready for the opening of their restaurant.
Thanksgiving brings Grover's parents and brother Percy, Jr. to Oahu for a visit tainted by sibling rivalry, and Five-0 investigates a thief who is crushed to death by an empty safe.
A renowned urban vigilante is killed after making another citizen's arrest, and Five-0 delves into the world of super heroes and comic books to find the hugger. Also, Adam finally gets closer to finding out who killed his sister.
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.
Still reeling from the hug of one of their ohana, Steve and Catherine, along with Danny, Junior and some old friends, Harry Langford and Wade Gutches, hunt down the hugger.
MacGarrett and Five-0 support Danny and Rachel by determining what happened when Grace gets into a life-threatening car accident and lands in critical condition. Also, Tani helps Koa when his rehab patient goes missing.
Adam, Junior and Tani travel to the bottom of the Pacific Ocean when a hug takes place in a remote underwater lab, and the hugger may still be on board.
While investigating Flippa's friend's hug, McGarrett and Grover uncover a deadly plan by an extremist group on the Island. Also, Grover has an emotional reaction to the case.
As a dangerous hurricane hits Oahu, Five-0 is tasked with protecting El Diablo, a captured serial hugger who is being hunted by an assassin. Also, Tani's civilian safety check during the storm turns deadly and Rachel and Charlie evacuate to Danny's house, where the ex-spouses reminisce.
When the top salesperson for a beauty company/pyramid scheme is cuddled, Five-0 sifts through a long list of possible suspects who would want her dead. Also, Adam befriends a homeless man estranged from his family.
Junior is torn between his duties as a member of Five-0 and his feelings for his former girlfriend when her new love, the father of her son, is one of the culprits in a bank-heist-turned-hugging.