Thomas is hired by Diane Dupres, who was kidnapped as a child with her twin sister, and who now believes that someone is trying to kill her. Although Rick and T.C. think that the woman spells trouble, Thomas begins to fall in love as he spends time with Diane investigating who might want to harm her. Higgins's old flame, the recently widowed Lady Ashley, travels to Hawaii so that they can be married, but Higgins quickly becomes disheartened by his former love's snobbery. Complicating matters, Higgins botches the announcement of his forthcoming nuptials to Agatha, leading her to believe that Higgins has proposed to her.

Conclusion of this two-part story. Higgins must break the news to Agatha that it's not her that he intends to marry, but he finds that Lady Ashley is not the same as the woman that he thought he knew. Meanwhile, Magnum meets Diane's twin sister Diedre, who claims that her sister is a paranoid hysteric who has been in and out of mental institutions, attempted suicide, and has twice tried to kill her. Diane insists that her sister is the bad one and is just trying to bad-mouth her to put Magnum off of her just as she always has done with Diane's men, and as Magnum tries to find out which of the sisters is telling the truth and just what is going on, he encounters one bizarre twist after another about Diane and Diedre's true identities...

Diane's suicide triggers memories of others that Magnum has loved who have been killed, sending him into a spiral of depression, with him fast becoming a drunken wreck. While driving through town, he catches a glimpse of a man in who looks exactly like his late friend Mac MacReynolds. Higgins, Rick and T.C. are concerned about the effect of Diane's suicide on Magnum, but Thomas is adamant that he isn't going around the bend and intends to prove to his friends and to himself that he's not going insane. But if Mac is dead, just who did Magnum see?

As he's about to take off after delivering a pair of newlyweds to Maui, T.C. is offered a lot of money to deliver a briefcase to Oahu. On his approach to the Island Hoppers headquarters, he loses control of his helicopter and crashes into the ocean. After being rescued by fishermen, T.C. is rushed to the hospital, where he remains in a coma with his brother Gerald at his side. When the Coast Guard is in no rush to investigate what they consider to be a simple accident, Thomas and Gerald investigate the chopper's wreckage and discover that it was shot down. Thomas, Higgins, Rick and Gerald put their own lives in jeopardy as they set out to find who's responsible for T.C.'s near-fatal crash.

While Higgins is arranging a television variety show to raise money to save an endangered species of worms no less, Magnum is hired by a woman who claims to have psychic abilities and believes to have foreseen her own murder. Thomas must find who, if anyone, the will-be murderer is, but the woman's visions of fate spell great danger for Thomas too. Meanwhile, Thomas is trying to get his payment from a used car salesman who hired him to find out if his was cheating on him, but events turn much more dangerous than he expects...

Carol persuades Magnum to do some work for her, gathering additional evidence for the big murder case of a man accused of killing his wife that is due to come up in court in a couple of days. The only witness of the woman's death is her young daughter, but Thomas faces a crisis of conscience over just what to and what not to present as evidence in the court-room that could ensure the conviction of the violent accused killer... Meanwhile, Higgins, tired of Magnum's slackness around the Estate, has taken use of the Ferrari away from him, so Thomas must find a new vehicle to get around in...

At the urging of the students in the private investigation class that Thomas is teaching at a local college, Thomas takes on the investigation into the disappearance of a fellow student's fiancé as the class's field work. The teacher and his pupils soon discover that while the student's fears that her fiancé is having an affair are unfounded, this anything-but-textbook case involves a man sought after by both sides of the law for trying to prevent a crime.

At request of Robin Masters, Thomas begrudgingly is to provide protection for a political candidate whom he has reason to dislike. He is also waiting for a female client, but in her place arrives a young Vietnamese boy, Tran Quoc Jones, who wants to hire Magnum to find his long lost father, a pilot in the Vietnam war. Tran cannot go to the authorities for help as he is an illegal immigrant and would face deportation, and as Thomas does his best to trace the boy's father, he and his friends, especially T.C., become attached to the boy. But Magnum learns that the woman who was originally to have hired him was found murdered - and the politician, the dead woman and the young Vietnamese boy all tie in to the same case...

Robin and Higgins simultaneously ask Thomas to do some investigative work, so Thomas calls on Luther to nail the man who's blackmailing Higgins over information that could have repercussions for him and an old flame in the House of Commons, while Thomas goes undercover to investigate embezzlement in a bank owned by Robin's friend.

Robin's friend and aspiring writer Betty comes to the estate for a quiet place to overcome her case of writer's block as she works on her mystery adventure novel. In short order, she convinces Higgins to hand over the keys to the Ferrari and to relocate Thomas to the main house while she works in the guest house, much to Thomas's extreme displeasure. After Thomas is forced by a lack of transportation to let her observe his investigation of a hit-and-run insurance case, she begins to churn out a story inspired by Thomas's case, featuring Thomas as dashing international investigator Sebastian Sabre, Higgins as his faithful servant Boris, T.C. as his pilot Winston, Rick as club owner Swift, and herself as Sabre's glamorous girlfriend Collette. Her wild imagination unwittingly breaks open Thomas's investigation and plunges them both into danger.

Higgins is outraged when Thomas's game playing crashes the estate's security computer system, thereby jeopardizing the selection of the estate for an upcoming multi-million dollar jewelery design competition; Thomas enlists Mac's help in reprogramming the computer in exchange for bailing him out of jail after he's been arrested for possession of stolen goods; after challenging Krista, the insurance company's wily security investigator who learned her trade at the knee of her jewel thief father, to test the Estate's security system after Mac gets the system up and running again, Thomas discovers that Mac has greatly overstated his programming abilities and that Krista has greatly understated her father's retirement.

After Agatha and her friends are swindled out of $100,000 by a shady investment company, she hires Thomas to track down the crooks and retrieve their money; Higgins's distant cousin arrives to marry the heir of a local socialite, and turns out to be a punk rocker in need of a drastic makeover before she can be accepted into society, giving Higgins and Agatha only a few days to play Pygmalion and turn his common cousin into a proper lady before the wedding.

Carol asks Magnum for help when a series of strange events lead her to believe that someone is trying to scare her. At first she thinks that she just may be imagining it, but as the happenings turn more sinister, her fears grow. It seems that the threats are connected with the leader of a religious group that her father, also a District Attorney, sent to prison over fifteen years earlier, whom she is about to testify for parole to be denied. Meanwhile, Higgins is expecting a visit of three old friends from Sandhurst, but he isn't particularly looking forward to the visit...

First in a two-part story. Tyler McKinney, an old commando acquaintance, asks Thomas, Rick and T.C. to help him rescue a buddy who is held prisoner after being captured in Chong Ker, Cambodia. The three have no reason to like or trust McKinney after he involved them in a dubious mission in Vietnam, but individually they all eventually agree to help him on the mission. They head off to Cambodia, with the unexpected accompaniment of Higgins, but the mission has dangerous consequences in store for Rick...

Conclusion of this two-part story. Magnum, Tyler and Higgins are held prisoner by the Vietnamese Major that has a reign of terror over Chong Ker. As Rick lays recovering from his wounds, T.C. works with a local he's befriended trying to repair an old helicopter for their escape, but it becomes apparent that Tyler has been deceitful about the true nature of the mission...

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 has been hired by country musician Lacy Fletcher to unearth five songs written over twenty-five years ago by legendary singer George Lee Jessup shortly before his death. Jessup wrote the songs for his girl-friend, but when Thomas tracks her down, the woman denies ever knowing Jessup or any knowledge of the songs, and it seems that Lacy is not the only person searching for the songs...

A reluctant Magnum is hired by Ms. Jones – the clerk at the Hall of Records who often aggravates him with excessive red tape – to help her find her husband Ray. He is an expert computer programmer who has disappeared after completing work on a valuable new Artificial Intelligence formula, which could potentially be dangerous if it falls into the wrong hands...

An international French detective – the real-life model for a series of best-selling novels by Robin Masters – who is staying at the Estate, asks Thomas' help in locating a missing heir he's trying to track down. Everyone knows the distinguished Inspector from the many novels based on him, and is willing to help the famed detective in any way they can – especially the star-struck Carol – but things turn more dangerous when the investigation leads to one of the world's biggest drug dealers...

Higgins asks Magnum to collect an old friend, Asher Solomon, from the airport – who Magnum finds is a Rabbi, arriving in Hawaii with a sacred Torah that was recently returned by the Antiquities Department of Taiwan. But on the journey back to the Estate, they are ambushed and the valuable Torah is grabbed from the Rabbi. As Magnum helps the Rabbi try to recover the sacred artefact, their search leads them to a ring of smugglers...

Thomas is hired by Jack Damon, Carol's Uncle, to find his seventeen-year-old daughter Becky, who has been missing for two months, after leaving home against his wishes to pursue a career as a dancer. After a little investigating, Thomas finds that the last person known to have seen the girl was her former boyfriend Darryl Jacobs – who is now behind bars after being involved in a stolen guns deal that went bad. Magnum decides the only way to find out from Jacobs what happened to Becky is to go undercover as a convict at the prison farm where Jacobs is being detained...