Danno and a college professor are kidnapped by a revolutionary group of young radicals led by a hardened criminal.

A geophysics expert, Bernard Brown, is heavily in debt, so he comes up with a plan to cause an explosion in the Hawaii Volcanoes National Park, which will cause lava to pour all down the hillside and into the city of Hilo, unless the Governor comes up with half a million dollars as a ransom.

Eddie Josephs is a paranoid schizophrenic who is carrying out murders based on old Five-O cases. McGarrett must follow his clues and catch him before more people die.

A sophisticated thief is selling his goods to legitimate businessmen, and Five-O must find a way of trapping him.

Senator Harlan Henderson suffers from multiple personalities, and one side of him wants to kill himself. However, he ends up blowing up his secretary, and McGarrett uses handwriting and a diagnosis from a psychiatrist to try to crack the case.

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.

When his son is beaten to death, a powerful cattle baron takes matters into his own hands, and McGarrett and Five-O must prevent the rule of law from breaking down.

A gangland execution investigation takes a turn for the peculiar when it is found that the victim had two identities.

Five-O must investigate why three infallible security systems are failing to prevent the theft of priceless artworks.

After an attempt is made on Steve McGarrett's life, he is drawn towards a female art dealer, but she too may not be good for his health…

Two conmen use a gang of Five-O lookalikes and doubles to extort money from Honolulu businessmen.

Wo Fat returns to Hawaii in order to have a Chinese diplomat whom he classes as a foolish peace-maker assassinated.

A Honolulu murder is mysteriously linked to a human fossil smuggled out of China in the Second World War.

An investigation into a murder is sent off track through the modification of computer information, and Five-O must use the latest technology to rescue the case.

Three women desperately in need of money take to armed robbery of tourist buses as a way to raise some quick cash.

When a young boy is arrested as a witness to a murder, McGarrett must contend with a fiery deputy public prosecutor.

A million dollar reward for the return of five figurines sparks off a trail of murder and theft that leads to Hawaii.

When a psychotic man kills his doctor, Five-O must use a unfinished painting to gather clues to his whereabouts.

An elaborate sea and air scheme for heroin smuggling goes unnoticed until one of the gang tries to sell out their plan for a fix of heroin.

McGarrett must prevent a mob war by tracking down an unknown hitman and his intended target.

When a deranged ex-Army officer shoots a policeman and takes a young girl hostage, McGarrett disagrees with a police captain over the best way to free her.

A Saturday Night Special passes from person to person and causes Five-O trouble and others misery.

Five-O works with a air traffic investigator in order to put a stop to illegal ticket sales which have already cost several lives.