A notorious thief is sprung from prison by a criminal gang who wants him to teach them how to rob a diamond exchange and escape undetected. The thief obliges, but McGarrett and Danno are puzzled when the thief -- who ought to be hiding as deep as possible -- is spotted at a drugstore and at a marina.
A war hero back from Vietnam dies under mysterious circumstances. Was it a murder or a suicide? For McGarrett, finding the truth is no easy matter, as neither the victim's family nor the U.S. Army are willing to cooperate.
The Chinese (led by Wo Fat), the Soviets (led by Mischa Toptegan) and assorted criminals are all after perfect counterfeit plates. The plates were originally developed by the Chinese, who want to use them to flood international markets with phony U.S. currency and destroy the American economy. Jonathan Kaye enlists Five-O's help to track down the plates and a Navy intelligence officer, and a friend of McGarrett's, also is part of the probe. However, the Navy man is secretly working with Nicole Fleming, one of the criminals after the plates.
U.S. Commander Nicholson now has the perfect counterfeit plates. His price: $2 million and amnesty for all crimes (including the murder of the man he got the plates from). His girlfriend, Nicole Fleming, is playing the Chinese and Soviets off each other before striking a $3 million deal for herself with Wo Fat. McGarrett and Five-O are running out of time to recover the plates.
A group of masked men break into the home of an international arms dealer and kidnap his wife. McGarrett soon realizes the case is far more than a simple kidnapping - he's now involved with agents of a foreign civil war.
A man, who had been a witness in a murder trial, dies mysteriously down at the waterfront. McGarrett thinks he was murdered and that his death was tied to the murder conviction of a formerly prominent politician.
A young man in Oahu State Prison has been a model prisoner and is let out on parole. A few days later, he appears in Five-O headquarters at the Iolani Palace, taking prisoners and demanding that Dan Williams be brought to him. All of this is transpiring while McGarrett is on the Mainland. Danno has no idea why the man wants him dead. It is not until Williams enters the trap that he discovers the man is the brother of a man the lawman killed in season one's "...And They Painted Daisies on His Coffin."
Gary Phillips, the mentally challenged son of baseball star Lon Phillips, encounters a woman while on his way to the concession stand during a ball game. She turns up dead shortly there after. Was he responsible? Or does he know who was?
Gary Phillips, on the run and afraid of the police, narrowly escapes a murder attempt. McGarrett & Co. begin to piece together what really happened at the ball park. But the real killer is still determined to silence Gary.
Two skeletons, a man and a woman killed ten years ago, are discovered. One of them comprise the remains of the former right-hand man of Mondrago, a prominent businessman. McGarrett concludes Mondrago is hiding something and may have killed his late wife and his former business associate. Mondrago is indeed hiding something, but not what it seems. The key to the mystery is Mondrago's daughter, who looks just like her late mother.
McGarrett must figure out how to get the goods on a mobster who is trying to clinch a mainland deal while murdering his enemies (including a past girlfriend) and putting them in an incinerator, which wipes out all traces of their existence -- or does it?
Several women have been strangled in Honolulu. The pattern in all of the cases was that after each killing, the killer would put make-up and a wig on each victim as if he wanted her to look like a prostitute. Also, in each case except for one, the killer seemed to have a key to the house of his victims. However, the one exception was the home of a private investigator whose wife was killed. It is eventually theorized that the killer is looking for a prostitute who he was obsessed with.
A cagey professor and the syndicate team up on a deadly caper. About $750,000 in traveler checks are stolen in Denver. A planeload of criminals posing as academics board a charter flight to Honolulu, with each given $7,500 in traveler checks to spend. A hit man ensures a woman employee of the Honolulu office of the traveler check company can't get the serial numbers of the hot checks circulated. McGarrett calls the caper a "jigsaw puzzle." The question is whether he can solve it in time.
Two hippies, panhandling for money, decide to approach a tourist. The first hippie, a young woman, is rebuffed. However, the tourist comes on to the second, male hippie. The hippie freaks out and hits the tourist on the head with a board, taking the man's wallet in the process. The wallet contains a key to an airport locker, which contains a briefcase full of money. It turns out the tourist is an embezzler who will do anything to get the money back.
A mentally disturbed former soldier buys a new rifle and ammunition after a sales clerk fails to check him out. The soldier even signs his name as "George C. Patton." He then holes up in a spot on Diamond Head and shoots out the tires of a motorist's car and proceeds to shoot two police officers, one fatally. McGarrett coordinates the police response. The more McGarrett finds out, the worse it gets. It turns out the sniper has a weird relationship with his mother. The mother, in turn, denies the former soldier is her son. Time is running out and Five-O must prepare to...
A shipping company which runs lots of valuable cargo through the islands is cherry-picking the most valuable items, taking them out of the shipments, and selling them on the black market. They also have a habit of killing anyone who gets too close to their operation. Their fatal mistake is stealing a quantity of medicine which is the only thing that can save a toy manufacturer's critically-ill wife. When the emergency re-order arrives too late, the husband -- who has been cooperating with Five-O -- goes off on his own to seek vengeance.
A gang, led by the vicious Hawkins, is executing a plot to steal $6 million. The group includes a bank employee and an alienated, long-time employee of a trucking company. The plan results in multiple deaths. Dan Williams leads the Five-O investigation because McGarrett is having to testify at a trial on the "Big Island."
The wife of a wealthy doctor is shot to death. The physician seems to have a tight alibi while clues point to another man. But the more Five-O probes, the more the obvious turns out not to be. The suspect is arrested while trying to fence the dead woman's jewelry. But he was dying and had little motive to kill the woman. McGarrett & Co. need to dig deeper to find the truth.
McGarrett gets a telephone call upon arriving at work. The caller says he intends to kill someone. The caller has also sent the lawman a key that will tell McGarrett the identity of the target. Danny and Kono have received other clues at their homes, one of which is a photograph of Chin Ho's garage. The clues are a mixed bag, including several false leads. The caller continues to taunt McGarrett, finally revealing that the intended victim is the Governor.
French McCoy, thug for a Miami mobster, turns up dead (stabbed in the chest) and mutilated (one of his pinkie fingers cut off). The mobster, known as "Big Uncle," was looking to move into Hawaii. One of four Hawaiian mobsters is responsible. McGarrett must figure out which one before a gangland war erupts.
Willy Stone, a punch-drunk former boxer, attacks a young fighter for no apparent reason, breaking the younger man's hands. Edmonds, a Detroit hood, has invested much in the young boxer and is enraged when he finds out the boxer can never fight again. Five-O seeks to find Willy before Edmonds can extract his revenge. Meanwhile, Edmonds has summoned a hit man from the Mainland to kill Willy.
Someone calling himself "Kahili" (the Hawaiian god of battle) wages his own personal war against polluters. At first the pranks are bad but not dangerous, like climbing a ladder to the top of a huge chimney with a 125-pound ceremonial shield and capping the chimney (thus blowing out the furnace inside and chasing everyone out of the factory). However, Kahili's actions get steadily more violent. After blasting a crop-dusting plane with a shotgun (he pulls the pilot to safety), Kahili types up a list of the five worst polluters in Hawaii and entitles it "Kahili Death ...
When famed bank robber Lewis Avery Filer, whom McGarrett put away a year and a half ago, learns that a fellow con about to be released plans to resume his career as a drug dealer, he decides to get out on his own and infiltrate the drug gang. Filer plans to tail the drug dealer and relieve him of the $4 million he's received for cocaine shipments, through use of trickery and gadgetry. McGarrett tries to outwit Filer once again and recover the money before Filer can flee with it.