A local thug, Piro Manoa, is trying to create the impression of corruption in the Five-O force, and Duke is implicated in a murder. McGarrett and the team, with new recruit Ben Kokua, must save Duke's position and work out the plot of the organisation behind the false accusations.

When two of a egotistical racing driver's support staff are murdered, suspicions of sabotage fall upon his attractive girlfriend.

A private investigator, Sam Tolliver, arrives from Texas to help an old friend who is being blackmailed and is at risk of being killed if he doesn't pay up, but he ends up wanting to become part of the blackmail operation.

Danno shoots an apparently armed teenager but finds that he was mistaken, and public opinion and the teen's brother turn against him. McGarrett must act to defuse the potentially explosive situation.

Wo Fat is suspected of being behind the theft of a mobile ICBM device, and McGarrett with other top officials must stop him selling it off to the highest bidder.

Army computer technician Jack Gulley kidnaps a scientist and then uses a planned heist by three accomplices on a military base to divert Five-O's attention from his sale of the scientist to the highest bidder.

A doctor tracking venereal disease is murdered, and Five-O must track the series of encounters to find out who is a carrier. Their investigation is made doubly important by the murder of a young woman who is close to a upcoming politician. He seems a likely suspect but McGarrett suspects a deeper plot.

Danno is found in the back of a truck, dazed and confused, and McGarrett and the others must help him piece together how he came to be in that situation.

McGarrett becomes involved with the Vashon mafioso family after the youngest member, Chris, is implicated in a daring raid on a hotel.

McGarrett must contend with Honore Vashon, who wants revenge for his son's death.

Dominick Vashon, the patriarch of the clan, makes his attempt to bring down McGarrett and Five-O.

When McGarrett arrests a group of vigilante nationalists, hidden bombs at the courthouse threaten to destabilise the islands.

A husband and wife team of scam merchants get caught between some of Hawaii's most powerful mobs.

McGarrett agrees to let Toni, a tough female convict, get married and have a honeymoon in protective custody as long as she will testify against a local hood.

A crazed electronics wizard threatens the lives of a psychiatrist and his patients by using electronic devices and gadgets.

A senior partner in a stock exchange firm comes up with a foolproof plan to rob the Honolulu Stock Exchange.

McGarrett and company must break through a tissue of lies in order to protect a Russian defector from being killed.

Two simple criminals kidnap a young girl, and hide out in a bunker at Diamond Head. McGarrett must unravel the reason why they are there and get the girl safely away from them.

A travel agent who operates gambling trips is killed in order to send a warning to others that the syndicates will not tolerate competition.

Chin Ho must face the fact that his daughter, Alia, is in love with the son of a local criminal under investigation, and that she plans to get married to him.

A burglary at the home of a well known island family sets off a series of events that ends in murder.

A single person is holding out in a Five-O trial, and McGarrett and the team have to find out who is stalling and why they are doing it.

A amputee with no hands sets out to kill every police officer who contributed to his injury, and that includes Steve McGarrett.

Murders are being committed seemingly at random every six weeks, and McGarrett is at a loss to understand the motives for these crimes. However, a newspaper may hold the answer.

When a large amount of diseased rats are found on a boat with all the crew dead, Five-O must contend with an outbreak of bubonic plague.