After the brides of three G.I.s killed in Vietnam turn up dead, the Five-O team uncovers an insurance scam run by a sergeant with a murderous grudge. Harry Guardino, BarBara Luna, James Hong, Barbara Nichols, Loretta Swit guest star. NOTE: The ending credits change from a flashing blue police motorcycle light to Hawaiian outriggers. This sequence is used all the way to the series finale.
Taking place on December 6 and 7, 1969, a Japanese ninja (Mark Lenard) who had been in a mental hospital since December 6, 1941 plans on carrying out his mission from 28 years earlier. NOTE: Patricia Tuscano as McGarrett's secretary, Jenny Sherman.
Fear spreads through Hawaii after rumors of a supposed imminent tsunami, but McGarrett discovers the true threat: the villainous Red Chinese agent Wo Fat has kidnapped a renowned geneticist (Will Geer) and plans to use the scientist's discoveries to create a superior race. NOTE: Peggy Ryan as McGarrett's secretary, Jenny Sherman. In Season 1, Ryan portrayed the governor's secretary, Mildred.
A prostitute has been murdered by a gangster, but the sole witness to the crime -- a respectable small-town hardware salesman -- is afraid to testify. To catch the killer, McGarrett uses a beautiful undercover policewoman as bait. John Randolph, Albert Paulsen, Anne Helm, Elaine Joyce guest star.
After a band of foreign revolutionaries steal weapons from an armory, Five-O mobilizes to bring down the terrorists. Henry Silva, Julie Gregg, Edward Colmans, Tom Nardini guest star.
A psychology professor who is secretly an agent of Wo Fat is using the power of hypnosis to turn citizens into assassins. Steve McGarrett has to stop these mind games before he becomes the next target of the hypnotist. Eric Braeden, Marianne McAndrew, Khigh Dhiegh, Sheila Larken guest star. NOTE: Danny Kamekona as Che Fong. Also, this is the only time Wo Fat and McGarrett do not have a direct encounter with one another, though both appear in the same episode.
Hawaii's sugar industry becomes a terrorist target for germ warfare. Can Five-O stop the ensuing sabotage? Theodore Bikel, Soon-tek Oh, Philip Ahn, Linda Marsh guest star.
One of Hawaii's most treasured artifacts, the robe of the late King Kamehameha, is stolen. McGarrett pursues the theft to a group of anti-establishment university students. Brandon deWilde, Jennifer Leak, Randall Duk Kim guest star.
To nail a local gangster for murder, Steve McGarrett must travel to Singapore to transport the witness to the crime. The witness is an alluring woman (Marj Dusay) who is tired of running from her past.
Five-O investigates an ex-racketeer suspected of heading a local crime syndicate, but Steve McGarrett follows a hunch that the politician seeking to indict the accused man is involved in some dirty dealings of his own. James Gregory, Jason Evers, Keye Luke, Lyle Bettger guest star.
When the plane carrying a despised dictator is forced to make an emergency landing in Hawaii, the notorious leader is marked for death… and it's up to Five-O to protect him. Titos Vandis, Paul Stevens, Joe De Santis guest star.
After a kidnapped boy escapes his captors, the boy's father enlists Five-O to recover his ransom money from the extortionists. McGarrett's only lead is from the boy: "a frog and the devil". Frank Marth, Bill Zuckert, James Hong, Melody Patterson guest star.
The stakes are murderously high when a beach boy and a playboy vie for the attentions of a seductive heiress in a bizarre card game. Beverlee McKinsey, Kaz Garas, Eddie Firestone guest star.
After an adversary from McGarrett's past robs a bank under the noses of Five-O, McGarrett follows a trail to Hong Kong to nab the brilliant thief. William Windom, Philip Pine, Jackie Coogan guest star. NOTE: Harry Endo as Kaspar.
A surprise birthday party for McGarrett ends with a bang--a car-bomb explosion of his black 1968 Mercury Park Lane Brougham. The explosion leaves McGarrett blinded. As he recuperates, the Five-O team searches the islands for his would-be killer. Marion Ross guest stars. NOTE: Harry Endo takes over the role of Che Fong.
Five-O investigates the death of a yoga student who died while performing a dangerous yoga technique that calls for the student to asphyxiate himself. NOTE: This episode was barred from airing in syndication after a viewer reportedly imitated the deadly yoga technique featured in this episode and died. The episode is absent from both the season two DVD release and the complete series set, as well as from online streaming and digital downloads.
Two military policeman spot John Mala, a man who McGarrett has helped in the past, but who has gone AWOL. One of the policemen is shot, and tensions rise as Five-O and the army police clash in their techniques of investigation and their treatment of the local population.
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.
After a crooked card game leads to the murder of a young honeymooner, the victim's brother sets out to find the man responsible. Now Five-O must stop the vigilante before another murder takes place. Jack Soo and John Colicos guest star.
When Chin Ho Kelly is accused of taking a bribe from a drug dealer, the Five-O members defend one of their own. Martin Sheen and George Petrie guest star. NOTE: A clip scene of the shotgun murder from "All the King's Horses" is reused in this episode. Chin Ho Kelly has been with the police 22 years; has a wife and 8 children.
A cop's wife has been murdered. When the widowed officer (Tom Skerritt) seeks revenge, Danno, his longtime friend, tries to stop him. Sam Melville (actor) guest stars.
McGarrett encounters resistance from federal agents when he attempts to uncover the mystery behind the disappearance of a gullible research scientist from his important government post. Charles Aidman, Pilar Seurat, Ronald Long guest star.
A brilliant but emotionally unstable scientist has disappeared. He discovered a biological mutation which he calls "Q strain", which he plans to unleash as a protest against germ warfare. Ed Flanders, Loretta Swit, Joseph Sirola, Dana Elcar, Karl Swenson, H. M. Wynant guest star. NOTE: Joseph Sirola as Jonathan Kaye and would continue the role until Season 5.
Dr. Kline's deadly toxin is lost, he is having second thoughts about his plan, and McGarrett has to find the vial before it disintegrates and poisons the whole island. Already the toxin is doing its deadly work as innocent people come into contact with it.
A jewel thief masquerading as a socialite attempts to steal a priceless emerald, "The Queen of Polynesia", from the governor's gala. But Five-O are waiting for the thief--disguised as workers at the event. Joanne Linville, George Gaynes guest star.