The team investigates a centuries-old pirate story involving buried treasure; Gabriel kidnaps Kono and Adam on the morning after their wedding.
A bomb squad is attacked and the culprit threatens to detonate hidden explosive devices unless arsonist Jason Sinclair (Randy Couture) is released from prison.
A scuba diver is killed with a gun that was used in a recent murder; McGarrett gets ready to propose to Catherine.
A wealthy recluse's corpse is found in a field with almost $1 million in counterfeit bills; Adam is abducted and forced to torture one of Gabriel's men.
The team questions members of a stunt biker gang when a killer escapes by jumping his motorcycle from roof to roof; the team prepares for Tough Mudder.
On Halloween, the team tracks a serial killer inspired by an iconic character; a blood bank is raided by an armed gang.
McGarrett and Lynn's date on a deserted island turns deadly when a mob boss gets involved; a gambler abducts a high-school football star's father in hopes of forcing the athlete to throw a game.
A charming con man (Kristoffer Polaha) helps Five-0 look for the person who murdered his partner; a police inspector from San Francisco (Julie Benz) works with Chin on an investigation involving the murders of five arms dealers.
When a college professor is killed, Five-0 goes back to school with Danny, who is posing as the professor's replacement.
When a promising local boxer's brother is murdered, the prime suspect is an outspoken opponent -- the reigning champion.
Danny and McGarrett try to solve their partnership issues with a couples retreat in Maui; Kamekona's past comes back to haunt him.
A special personal mission sends McGarrett's Aunt Deb (Carol Burnett) to Oahu; unstable Japanese WWII bombs hidden on the island are stolen.
Grover goes to Chicago to get a confession from Clay Maxwell; Chin and Kono are held at gunpoint by people who don't know they are cops.
A double homicide occurs that involves infidelity; McGarrett and the team share disastrous Valentine's Day experiences.
Danny's mom is questioned by the FBI; McGarrett works with a young, autistic man who might be able to help solve a murder.
McGarrett turns to Odell Martin (Michael Imperioli) for help when a confidential informant is accused of murder.
A Russian spy steals a flash drive containing classified information that puts a Five-0 member at risk; McGarrett learns why Catherine left; Abby keeps her mission a secret.
The body of a man left for dead off the coast of Oahu leads Five-0 to a deadly slave trade business that is operating aboard a fishing vessel.
Grover is forced to take his family on the run when a dangerous mob boss seeks revenge for a 15-year-old case.
The team investigates the theft of high-tech indestructible suits made for the military; Jerry and his sister try to save a captive elephant.
When a deliberate chemical spill enables six dangerous inmates to escape, the team goes on an intensive manhunt to find them.
The team races to save an abducted college student from a dangerous vigilante; Max, Kamekona and Flippa struggle to survive after being shipwrecked.
The Five-0 team learns that one of its own has a deep connection to the young daughter of a woman who was murdered in her home.
Five-0 tries to protect a wounded Gabriel and plan an escape when enemy gunmen storm the dilapidated building in which Gabriel is trapped.