From Wikipedia:
Hawaii Five-O is an American television series that starred Jack Lord in the lead role for a fictional Hawaii state police department. The show ran for 12 seasons, from 1968 to 1980. The twelfth season was repackaged into syndication under the title McGarrett.
The CBS television network produced the program, which aired from September 20, 1968 to April 5, 1980. Currently, the program is broadcast in syndication throughout the world and on-demand streaming media via CBS Interactive. Created by Leonard Freeman, Hawaii Five-O was shot on location in Honolulu, Hawaii, and throughout the island of Oahu as well as other Hawaiian islands — with occasional filming in other locales like Los Angeles, Singapore and Hong Kong.
Hawaii Five-O centers on a fictional state police force (named in honor of Hawaii's status as the 50th State)[3] led by former Navy officer Steve McGarrett (Jack Lord), who was appointed by the Governor Paul Jameson (Richard Denning). McGarrett was assisted regularly by State Police officers — a young officer, Danny Williams (played by Tim O'Kelly in the show's pilot, but replaced in the regular series by James MacArthur), Chin Ho Kelly (Kam Fong) and Kono Kalakaua (Zulu). Later, Honolulu Police Department Officer Duke Lukela (Herman Wedemeyer) joined the team as a regular, as did Ben Kokua (Al Harrington) who replaced Kono. Occasionally, they were assisted by other officers on an "as-needed" basis. During the course of the show, the team was also assisted regularly by: medical examiner Doc Bergman (Al Eben), forensic specialist Che Fong (Harry Endo) and a secretary. The first secretary was May (Maggi Parker), then Jenny (Peggy Ryan) and later Luana (Laura Sode-Matteson).
For twelve seasons, McGarrett and his team hounded international secret agents, criminals, and Mafia syndicates plaguing the Hawaiian Islands. With the aid of District Attorney and later Hawaii's Attorney General John Manicote (Glenn Cannon), McGarrett was successful in sending most of his enemies to prison. One such Mafia syndicate was led by crime family patriarch Honore Vashon (Harold Gould), a character introduced in the fifth season. Blaming McGarrett for the death of his son, Vashon swore vengeance using all of the resources available to him. Most episodes of Hawaii Five-O ended with the arrest of criminals with McGarrett's catch phrase to Williams, "Book 'em, Danno!", with the offense occasionally added after this phrase, such as "-Murder one!". Other criminals and organized crime bosses on the islands were played by actors such as Ricardo Montalban, Gavin MacLeod, and Ross Martin as Tony Alika. For the 12th and final season, series regular James MacArthur had left the show (in 1996, he admitted he had got tired and wanted to do other things), as did Kam Fong. Unlike other characters before him, Chin Ho did not just vanish from the show but was murdered while working undercover, trying to expose a protection ring in Chinatown (last episode, season 10). Previously Chin's family who lived locally had been mentioned. In this episode, his wife had died and his daughter now lived on the (US) mainland. New characters Jim 'Kimo' Carew (William Smith), Lori Wilson (Sharon Farrell), and Truck (Moe Keale) were introduced in season 12 alongside returning regular Duke Lukela.
The Five-O team consisted of four to five members (small for a real state police unit) and was portrayed as occupying a suite of offices in the Iolani Palace. The office interiors were a soundstage set. Curiously, it lacked its own radio network, necessitating frequent requests by McGarrett to the Honolulu Police Department dispatchers to "Patch me through to Danno". McGarrett's tousled yet immovable hairstyle and proclivity for wearing a dark suit and tie on all possible occasions rapidly entered popular culture.
In many episodes (including the pilot), McGarrett was drawn into the world of international espionage and national intelligence. McGarrett's archnemesis was an intelligence officer of the People's Republic of China, Wo Fat. The Communist rogue agent was played by veteran actor Khigh Dheigh. The show's final episode in 1980 was titled "Woe to Wo Fat", in which McGarrett finally put his archnemesis in jail.
The show's action and straightforward story-telling left little time for personal stories such as wives and girlfriends, though a two-part story in the first season dealt with the loss of McGarrett's sister's baby. Occasionally, a show would flash back to McGarrett's younger years or to a romantic figure. The viewer is left with the impression that McGarrett, like Dragnet's Joe Friday, is wedded to the police force and to crime-fighting at this point in his life. Tee-totaller McGarrett often worked very late at the office, long after all others had gone home.
In the episode "Number One with a Bullet (Part 2)", McGarrett tells a criminal that "it was a bastard like you who killed my father." His 42 year old father was run down and killed by someone who had just held up a supermarket. Three days later at the funeral, 13 year old Steve McGarrett knew that he wanted to be a cop to stop such people.
Hawaii Five-O survived long enough to see reruns of early episodes enter syndication while new episodes were still being produced. The 12th season was repackaged into syndication under the title McGarrett.
Since McGarrett was also a commander in the U.S. Naval Reserve, he sometimes used their resources to help investigate and solve crimes, hence the Navy was credited in the closing credits of some episodes.