A band of young radicals is killing ordinary people at random. Five-O consults an academic who is knowledgeable about such groups. The group then kidnaps Dan Williams and the academic, threatening to kill both men. Larry Wilcox and Scott Marlowe guest star.
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.
A egocentric psychopath re-enacts murders featured in an article recounting the team's past crime-solving efforts. Danny Goldman and Ivor Francis guest star.
While Hawaii Five O investigates the murders of both an undercover federal officer and a HPD Detective killed during two hijacking operations, Mcgarrett matches wits with a fence who sells stolen goods to legitimate industries solely by telephone. Ray Danton, Jacques Aubuchon and Casey Kasem guest star.
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.
A cattle baron (Leslie Nielsen) seeks revenge when one son (Perry King) says another was killed. Bruce Boxleitner also guest stars.
An autopsy reveals that the victim of a gangland slaying led a double life. Jessica Walter, Sam Elliott and Abe Vigoda guest star. Real-life Honolulu Mayor Frank Fasi has a cameo. NOTE: This is the last sequential appearance of Al Harrington as Ben Kokua. After this episode, he appears in sporadic episodes for the remainder of the season and is removed from the opening credits of episodes he does not appear in.
Thieves break through three security systems to steal art from a millionaire. Gail Strickland, George Voskovec and Luther Adler guest star. NOTE: Al Harrington does not appear in this episode. Doug Mossman begins his regular series appearance as Frank Kamana.
In his search for the mobsters who injured him, McGarrett becomes romantically involved with a lovely fellow victim. Carol White and Ivor Barry guest star. NOTE: Al Harrington does not appear in this episode.
A businessman accuses the Five-O squad of demanding $100,000 in protection from him, and McGarrett suspects that impostors of him and his team have duped the businessman. Cameron Mitchell and Frank Gorshin guest star. NOTE: James MacArthur plays both Danny and his impostor. Doug Mossman appears as nightclub owner Al Shatner.
A traveling circus provides spy Wo Fat with the opportunity to attack a visiting Chinese foreign minister who is under Five-O's protection. Khigh Dhiegh, James Hong guest stars. NOTE: Al Harrington does not appear in this episode.
McGarrett investigates the murder of a wealthy Japanese business man which was so done as to resemble an act of hara-kiri (seppuku).
A Honolulu death is linked to the disappearance of a valuable human fossil (Peking Man) from China just before Pearl Harbor. Vic Tayback and Keene Curtis guest star. NOTE: Al Harrington does not appear in this episode.
A computer programmed with erroneous information points McGarrett's murder investigation to the wrong person. NOTE: Al Harrington does not appear in this episode.
A trio of debt-plagued women go out and rob tourist buses for money. NOTE: Al Harrington does not appear in this episode.
A deputy public defender criticizes McGarrett after he arrests a poor child (who has witnessed a murder, and is being taken into custody for his own protection) for a petty theft. France Nuyen and Bert Convy guest star. NOTE: Al Harrington does not appear in this episode.
Five priceless figurines are stolen and a million dollar reward sets off a chain of murder. Don Knight and Harvey Jason guest stars. NOTE: Al Harrington does not appear in this episode.
An unfinished painting leads Five-0 to a psycho (Richard Hatch) who murdered two doctors and a wealthy mainland business man. Gretchen Corbett guest stars. NOTE: Al Harrington does not appear in this episode.
A heroin smuggler is slain before he can sell information to the police. Ed Flanders, Bruce Boxleitner (making his second guest appearance this season) and Jo Ann Harris guest star. NOTE: Al Harrington does not appear in this episode.
McGarrett is out to stop a gang war by hunting down a hired gun. Nehemiah Persoff, Sal Mineo and Tommy Sands guest star. NOTE: Al Harrington does not appear in this episode.
McGarrett clashes with a police captain over Five-O's handling of a hostage situation concerning a teenage girl hostage and emotionally unstable war veteran. Linda Purl and Scott Brady guest star. NOTE: Al Harrington does not appear in this episode.
A mysterious .25 caliber "Saturday night special" causes citizens to kill which leaves a bloody trail of four murders; a car hijacking, an accidental shooting, two holdups and misery. Five-O must find the gun and uncover the gun smugglers to stop the carnage. NOTE: Al Harrington does not appear in this episode. Final appearance of the character Frank Kamana.
Five-O works with a air traffic investigator in order to put a stop to illegal ticket sales which have already cost several lives.