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.

A university professor, Dr. Paul Farrar, is using hypnosis to programme students into becoming assassins. McGarrett uses a policewoman as bait for Dr. Farrar, but the plan goes wrong and her life is put in danger.

A psychiatric worker, George Loomis, is trying to drive a fellow Vietnam veteran Ted Frazer crazy in order to cover up the fact that he massacred his own platoon during an action. Loomis kidnaps boys and drugs Frazer to make it look like Frazer is mad and to blame for the tragedy. McGarrett and the team must unravel this web of lies and clear Frazer.

Chin Ho is accused of bribery, and cannot provide alibis for the nights in question. Worse, he is called to the middle of nowhere for a set-up. Chin's position is threatened, and the Governor orders an inquiry. McGarrett and the others must work out how Chin was framed and clear him of the accusations.

The hitman sent to kill the witness to a two year old murder instead falls in love with her and McGarrett and the team must lead the search to find her before duty overtakes love.

Five-O search for the criminals who have set up Hawaiian singer and ecologist Jimmy Nuanu as the fall guy for a sewage plant bombing.

An electronics genius is busted out of prison so he can mastermind a massive robbery of diamonds from the Honolulu Diamond Exchange.

Five-O investigates the death of Vietnam hero Jack Rigney, who fell from a balcony. His father is a World War II veteran, but his brother Michael is a peacenik, and Danno goes undercover as a draft dodger to help solve the mystery of Jack's death.

Danno's past comes back to haunt him when the brother of a young boy he shot is released and wants revenge. The brother takes Chin Ho, Jenny and others hostage in McGarrett's office and threatens to blow them up, and Danno must resolve the tense situation.

A baseball player, Lon Phillips, brings his backward son to Hawaii to escape threats on his life on the mainland.

The son of the baseball player becomes the vital witness in a murder, but he is reluctant to tell either his father or Five-O of the crime.

McGarrett finds holes in a convict's story and a husband becomes a suspect in the murder of his wife.

A policeman who was kicked off the force blames McGarrett and Five-O and plans to kill the Governor.

A veteran criminal who has already had dealings with Five-O escapes, and plans to steal millions of dollars from drug smugglers.

A young widow becomes part of a blackmail plot involving the murder of a Chicago mobster.

A mock military emergency leaves a bank open for a robbery, and Five-O must travel to the opposite side of Oahu to find out more in their investigation.

A criminal, Hobart, is robbing liquor stores using a policeman's former gun, but the officer wants it back as he used it to kill a bankrobber five years before and the body has been uncovered.

McGarrett and Five-O need to find out why a Japanese banker ritually killed himself and catch a true criminal into the bargain.

McGarrett must solve both a mysterious kidnapping and the problem of having a nosy reporter analysing his every move.