Alex Kelsey, a lawyer involved with mobster Din Lee, kills a dying Japanese man. The dead man had been a Japanese operative at the time of Pearl Harbor. Kelsey believes the dead man had a secret stash of gold. Kazuo Tahashi, the dead man's son, arrives from San Francisco. But Tahashi isn't all what he appears to be, either. Meanwhile, in the background is retired U.S. Navy Commander Reginald Blackwell, who had been an operative in Naval intelligence. McGarrett & Co. must try to put the pieces of this jigsaw puzzle together.
Five-O is protecting Billy Madrid, lieutenant to a crime boss who will testify in an upcoming trial. McGarrett is wounded when a sniper shoots at Five-O officers escorting Madrid, an indication that the crime boss wants Madrid dead. But when the trial actually starts, Madrid tells a different story -- that McGarrett forced his testimony. Now, McGarrett & Co. must find a way to recoup or else the crime boss will go free.
Five-O begins an investigation after it's discovered a new trade center, destroyed in a massive fire, was constructed of sub-standard materials. The probe centers on Maynard, who works in the local agency that inspects building plans and construction sites. Maynard has framed, and then kills, one inspector. Five-O attempts a sting operation with the cooperation of one building but that plan goes awry when Maynard realizes he is being recorded while soliciting a bribe.
While flying her brother's hang glider over Makapuu, Molly Taggart witnesses a friend's murder by a pair of local low life. Realizing that their crime was seen from the air, the thugs set out to kill the glider's pilot.
An Australian scientist is killed on a Hawaiian sugar plantation after discovering an inspect capable of wiping out the sugar cane there. The investigation leads McGarrett & Co. to a complicated plot hatched by crooked developer Sam Patton to buy the plantation for a greatly reduced price. Before Five-O can solve the case, the death toll will rise.
Two idealists plan to kidnap the son of a Japanese industrialist as a way to generate $1.5 million toward their dream of researching ways for man to live under the sea. They don't realize their confederate is really part of a Japanese terrorist group. She has no intention of letting the boy live. Five-O has to race against time. The kidnapped child is in an airtight capsule underneath the ocean and he has only a limited air supply.
A rich developer's wife has been kidnapped and an ecology activist has been implicated. But the activist is innocent and has been framed. McGarrett & Co. try to solve the crime and find the kidnapped woman. As the title implies, the developer's neighbor holds the key to the mystery.
A series of gold robberies has hit Oahu. The operation is being run out of a halfway home for boys and young men. McGarrett sends in an HPD undercover officer to the home to turn up some leads. The trail first seems to point to the home's administrator, an ex-con. He turns out to be innocent. But Five-O's investigation is pressuring the organizations of the robbery ring.
Wo Fat, disguised as an academic from Hong Kong, organizes the theft of deadly toxins on loan to the University of Hawaii for medical experiments. McGarrett travels to Hong Kong in pursuit of Wo Fat but is captured.
The operator of a Honolulu museum devises a scheme: use the premier Hawaiian parade as the cover for the biggest bank robbery in Hawaiian history. First he kills a history expert who would know he was fudging the details of the recreation of the 1889 Wilcox rebellion. He also recruits criminals who can execute his plan. Once the caper occurs, can McGarrett & Co. rebound to bring the criminals to justice?
The wages of sin are death for prostitutes who are being murdered by a pimp and his totally psycho helper in an effort to get the survivors to join his "stable." The women organize on their own and try to fight back, but are reluctant to go to the police because they could spend a long time in jail. But as the frequency and viciousness of the attacks increase, McGarrett establishes a tenuous pipeline to the women's leader to try to trap the enforcer.
A group of university students and their professor are examining a volcanic crater when they discover the bodies of five men in an inconspicuous location. Doc Bergman is initially unable to determine the cause of their deaths, so he enlists the aid of cantankerous physicist Grant Ormsbee, with whom McGarrett and Five-O are already familiar (from the previous season's "The Defector"). Five-O eventually learns that most of the dead men came from a variety of foreign countries, and that all of them died from exposure to radiation - creating an even bigger mystery for ...
A plane arrives in Hawaii with 300 passengers aboard, including a tour group of 40. After everyone has left the plane, however, a stewardess discovers that one remaining passenger is dead, the victim of a stabbing with a thin instrument of some kind. Then a woman is discovered dead in a tropical park with a similar wound. Because the victim on the plane turns out to have been a CIA agent, McGarrett contacts Jonathan Kaye in Washington, and learns that the killer may be a mysterious hit man known only as "Raymond." With little information about either the killer or his...
Someone breaks into Five-O's temporary offices at the Territorial Building and, for the most part, manages to avoid the burglar alarms. When the alarm is triggered, the guard who responds is decoyed by a small music-playing souvenir doll long enough for the burglar to escape. The next day, however, Five-O's staff can find nothing missing, even though there is evidence that the lock to one of the cabinets was picked. What was taken they only learn later -- a single sheet official requisition form that is used to steal about $14,000 in state money -- the first step in ...
In an episode based on a real-life case (the villains on this show are even WORSE than their real-life counterparts), a gang of hijackers sign on as crew members of luxury yachts, then murder the owners and steal the boats to sell in South America. Danno and Sandi Welles go undercover to track them down, but Sandi is taken hostage on one of the boats. The title of the episode comes from the particularly sadistic gang leader flipping a coin to decide whether Sandi and the other hostages, whom he's going to throw overboard, will be given a life raft (this is also taken ...
A man named Jim Spier breaks out of prison, shortly after refusing to accept parole for the second time. Spier had been convicted of the murder of his wife, but had always claimed to be innocent of the crime. With assistance from a beautician friend of his, Spier changes his appearance and begins to investigate the case against himself anew. McGarrett and Five-O also look into the crime again, even as they search for Spier - and find that upon re-examination, at least some of the evidence against Spier doesn't appear to be that solid.
An extremely violent episode in which two seriously loco mobsters wage war on each other, with Danny's photographer girlfriend -- who snapped a picture of one of the two sneaking back into the Islands -- caught in the middle. The only show for which Seth Sakai received guest-star credit (he plays the second mobster, who snaps his fingers to get ice cream literally on call) is the one that debuts his shaved head (it was filmed after "Target: A Cop"); he would use the cue-ball look for the rest of the series.
The top financial aide to Chang Liu, the head of one of the islands' crime syndicates, is ambushed and killed when he tries to return to Hawaii surreptitiously via helicopter. The killers are all members of a street gang that normally wouldn't take on a criminal organization like Chang Liu's, but the gang members have inside information given by someone close to Chang Liu - his daughter. Then Chang Liu and Five-O each try to find the $4 million in laundered money that Chang Liu's aide was bringing with him when he was ambushed.