Season 1

Red Chinese agent Wo Fat uses a sensory deprivation chamber to procure information from U.S. agents. Steve McGarrett, head of Hawaii Five-O, investigates the death of a close friend who appears to have drowned. Steve's knowledge about his friend and a mysterious white substance lead him into a high-level intelligence matter involving a foreign agent. McGarrett, head of Hawaii's state police force, poses as "control," possessor of the names of other agents. He allows himself to be captured and placed in the chamber; will he be able to withstand the torture?

McGarrett is caught and cocooned, and must escape this torture and shut down Wo Fat's operation.

Victor Reese and his wife Nora are conning rich widows out of their savings, and then poisoning them and dumping them in the ocean. McGarrett and company hatch a plan to use a female officer to trap the duo.

Five-O probes into the death of an official who was instrumental in the development of the islands, and discovers a tangled web of lies and deception.

A young singer, Bobby George, plans his own kidnapping as a stunt, but when his father offers $500,000 for his release, his co-conspirators decide to double-cross him and take the money.

McGarrett and the gang must simultaneously protect a gangster from Japanese assassins and also try to convict him for his underworld activities.

Danny Williams is accused of shooting an apparently unarmed young boy. Meanwhile, in his investigation, McGarrett comes up against Big Chicken, a nasty dope dealer.

A woman buys fish from a monger, and is followed home and murdered. McGarrett and the team must discover who killed her and stop smugglers from completing their operation.

After a girl dies during a high speed chase, a trail of clues leads McGarrett to a Los Angeles prison, where he must act the part of convict Steve Crowley to gain the trust of his cellmate for a break-out, which will help reveal the plans of the crime.

When a singer, Joey Rand, finds that his career doesn't pay well enough, he turns to cat burglary. However he doesn't reckon on Hawaii Five-O.

A winning lottery ticket drags an army private into a the murky world of mob politics and vice.

When McGarrett is shot and badly wounded on a beachside jog, Danno and the team must work feverishly to find the culprit and prevent him from committing any more murders.

McGarrett must protect a protect a mob underboss so he is able to testify against his superior, Joe Matsukino. However, Matsukino has many tricks up his sleeve to silence his former colleague permanently…

When a young female student is found murdered on campus, suspicions fall on her boyfriend but McGarrett senses that something is not right.

Danno is taken hostage by a Vietnam veteran who is suffering delusional flashbacks and sees everyone as forces sent to kill him.

Young Eadie Hastings cannot be saved by Danno from jumping of a cliff, and Five-O think that she was high on speed. They track her source to a crank teacher, Professor David Stone, and Danno must pose as a surfer to investigate the drug pushers and users.

A man is found dead after having been robbed by a motorcyclist with a gun, and McGarrett is shocked to discover that the man was suffering from bubonic plague. The islands are quarantined, and the team must follow a series of clues to discover the cause of the outbreak.

Big Chicken returns in a tense prison hostage drama when McGarrett has to give himself over to the criminals as a bargaining chip and use psychology to take control of the situation.

When a girl is found murdered and numbered 'one', McGarrett suspects a serial killer. However the killer seems to be very selective in targeting members of a particular company, and suspicion soon falls on two brothers who stand to inherit the firm from their aged aunt.

When the boxing son of a policeman, Phil Kalama, is killed, he starts a personal vendetta, and McGarrett must both solve the crime and stop Kalama from committing another murder.

When the son of McGarrett's sister falls ill with cancer and she becomes involved in ‘naturology', her husband calls in Steve to investigate and persuade her to stop paying for the useless treatments. However, the quack doctor sets up a court case to prevent McGarrett from closing her practice.

McGarrett must use all legal means possible to win the court case against Dr. C.L. Fremont, stopping her fake treatments and saving his sister from more anguish and pain.

When a leader of a student peace movement is killed, McGarrett has to investigate the murder against a wall of silence and a distrust of the police by the activists.

Chin Ho and Dan Williams are tracking a safecracker but he pulls a gun and Danno ends up shooting him. McGarrett takes his identity of Harry Brown and must infiltrate a sophisticated gang of international thieves.

Sam Kalakua, a distant cousin of Kono, is being frightened into an early grave by an fake apparition of a Hawaiian god created by his nephew, who wants to sell the estate to a land merchant.