Magnum is hired by an attractive ""ghost writer"" who is writing a biography of eccentric millionaire Harold Farber - whom she has never met in person, communicating only via phone – when all her notes on Farber are stolen, in an obvious attempt to stop the book ever being written. As they investigate, they find themselves in the middle of a highly mysterious situation. Meanwhile, T.C. has landed himself a highly lucrative but shady piloting job delivering chemicals to a high-rise, but the building he is making the deliveries to turns out to be at the centre of the mystery...

Under protest, Thomas agrees to chaperone Rick's visiting 22-year-old sister Wendy while Rick works at the club, and quickly discovers that she's not the convent school innocent her brother thinks she is; after Wendy gives him the slip, Thomas scours the city searching for her and is devastated when the police find her murdered in an alley; when Rick blames Wendy's death on Thomas, the relationship between the men is dealt a severe blow, and Thomas vows to find her killers, even though Rick is determined to do the job himself with the help of information and an Uzi provided by Ice Pick; Thomas and T.C. follow Rick to Molokai, where the murderers are killed in a fiery crash as they are pursued by the three friends; to spare Rick's feelings and ease his grief, Thomas tells his friend the convincing lie that Wendy was a good kid who was just in the wrong place in the wrong time, instead of the truth that she was a drug mule murdered by the men for whom she worked.

Higgins persuades Magnum to help Garwood Huddle, a member of a notorious group of 1940s bank robbers, whom Higgins feels indebted to after Huddle had once assisted him in a daring MI6 assignment. The man, who has always seen himself as a modern day Robin Hood, has escaped from prison to rescue his kidnapped grandson, but they find that the stash of years-old stolen money that Garwood is to pay the ransom with is gone...

Mac's latest shady money-making scheme has landed him in trouble with the Japanese Yakuza, so he convinces Rick to buy a sailboat from him, complete with a crew of three Japanese women who barely speak a word of English. Rick is furious when Mac skips town just before the boat is impounded because Mac didn't own it in the first place, leaving Rick unable to repay Ice Pick the $20,000 he borrowed to buy the yacht, now that he can't make the money he planned by renting the boat out for charters. To get Rick's money back and keep the Yakuza and Ice Pick from doing him harm, Thomas sets out across the mainland to track down Mac.

Magnum is hired by meek insurance salesman Dan Wolf to locate his father, who he has not seen for thirty years. But unawares to Thomas, the client is actually an impostor hit-man who is using Thomas to help locate his victim, wealthy businessman Theo Wolf, whom he plans to kill to make a name for himself. In the hit, Magnum too is shot, bringing him close to death. Despite his wounds, Thomas becomes hell-bent on going after the hit-man to claim revenge for the dead man's widowed wife and son – and for himself...

T.C. and Magnum are fighting the demolition of T.C.'s club-house for underprivileged and troubled youths, which has been ordered to be destroyed by a greedy, obnoxious local land developer - even though he doesn't use the land. Their seemingly no-win struggle only results in a brush with the law. Meanwhile, unbeknown to them, Rick, on a trip away, wins the $1,000,000 jackpot in the Western States Lottery. Now a rich man, he meets a young woman who becomes his fiancée, but with his new wealth, he begins to neglect his responsibilities at the King Kamehameha Club, and gets mixed up with a couple of crooked poker players. Rick is so wrapped up in his whirl-wind new life that he risks loosing his job, and even more importantly, his friends, not to mention his newly acquired wealth...

At the 14th Annual Convention of Private Investigators, Magnum is to receive the 'Local P.I. of the Year' award, but the event is brought to a halt when Jean Claude Fornier, the famous French Detective, suddenly drops dead while giving a speech, after being poisoned. Magnum is helped - or rather, hindered - by several fellow crime-busting acquaintances as he seeks the murderer, and becomes entangled with a gang of drug smugglers, that the Inspector was hunting before he was killed...

Magnum is working on a case before a date with Rick's visiting cousin, when he sees a young native Hawaiian girl become an accidental witness to a murder. With the gun-man after her, Magnum saves the young woman as they escape by diving into the sea, and is injured with a gun-shot wound in the process. He regains consciousness several days later on the remote, secluded island of Kapu, after being rescued by a native fisherman from the island, and suffering from a hazy memory of the incident. There is no sign of the girl, and the island natives insist that he was the only one found. Thomas tries to remember the events that lead to him being on the island, and what has happened to the girl, but as he tries to uncover the secrets of the island and its people, it begins to seem more and more as if they don't want him to find any answers or to leave... Meanwhile, the killer is still looking for the girl, to eliminate her as the only witness to the killing...

While Rick is planning a surprise birthday bash at the Club for Ice Pick, Carol asks Thomas to observe a court case she is presenting before Judge Kearns, who drops the case on a simple technicality. She considers the Judge to be her mentor, but is concerned that of late he has been acting uncharacteristically, and suspects him of taking bribes to dismiss cases. She asks Thomas to help her hopefully disprove her worries. But the investigation sees turns up evidence that implicates Ice Pick, who in turn faces having to implicate the woman he was in love with decades earlier, who is now involved with a crime ring. Carol, Rick and Ice Pick must all face up to the weaknesses and mortality of their mentors and idolised ones...

When Ice Pick suddenly vanishes, Rick insists that Thomas find him. But things get complicated when Rick is arrested for allegedly killing a hitman who was contracted to murder Ice Pick -- and readily admits to the crime.

Thomas is running an errand to a local museum for Higgins' upcoming pageant for the Anglo-Hawaiian Historical Society, when he catches sight of a woman attending a funeral who, he soon learns, resembles a beautiful Hawaiian princess who tragically died in a fire in 1910. Thomas becomes enamoured with the elusive beauty, and experiences visions of himself, in 1900s naval uniform, with the woman. The mystery grows even more when he receives a package in the mail containing such a naval uniform, and a locket holding photographs of what looks like himself and the princess... Is Magnum once again experiencing something ethereal, or is somebody using the story of the princess to their advantage?...

As Rick's wedding looms ever closer, Thomas continues surveillance on Linda to catch the psychopathic killer who is stalking her; T.C. faces a reconciliation with his estranged wife; Thomas gets surprising news about his theory that Higgins is really Robin Masters, as well as the true fate of Lily.