Magnum returns from a case to find that Higgins' old Army commander is staying on the Masters Estate, under tight security, until some IRA members he helped capture are tried. Two Secret Intelligence Agents hire Magnum to protect the Brigadier and foil assassins out to kill him before the terrorists' trail, but the ""need to know"" basis the Agents insist on operating by only serves to complicate matters for Magnum...

When a beautiful model-actress is killed by a shot-gun blast, in a scenario closely resembling a scene from the script of an upcoming film, it is seemingly suicide. Magnum is hired by her former producer and lover to investigate any other men that she may have been seeing before her death – a case that Magnum is reluctant to take, but, feeling guilty for not taking it before the girl was killed, he agrees. But as the investigations unfold, it becomes apparent that there is much more to the case than first appears, and the supposedly murdered woman was being hounded by the obsessive former lover... The case reaches it's pinnacle when Magnum, still haunted by nightmares of the Vietnam war in his dreams, finds himself reliving it in much more reality, in a deadly hunt down on a deserted tropical island...

Higgins volunteers Magnum's services to guard a wealthy socialite's quarantined dog, after the attempted dognapping of the canine. ""Sir Algernon Farnsworth"" soon finds himself to be the most wanted dog in Hawaii, when his former owner, ageing gangster Victor DiGiorgio, has need to get him back. Magnum and an animal regulations officer are soon on the run with Algie from the would-be dognappers - and the fact that the officer seems to be scared of dogs doesn't exactly make matters any easier - but just why does DiGiorgio want the mutt back so badly?...

Magnum is hired by a Supreme Court nominee to find the woman he married forty years ago, in 1941, on the eve of the raid on Pearl Harbour. He was a young Navy Ensign, she was a prostitute, and after their marriage they subsequently became separated in the bombings, with the Judge presuming her dead - until recently, after he has started receiving blackmail threats relating to an incident forty years ago... Magnum's investigations into the case are helped by the fact that Higgins wants a favour, and is being overly nice and co-operative in return...

T.C. makes a late-night flight to land on a tanker, but on the journey back he is cornered arrested by the Coast Guard for transporting drugs. Magnum and Rick are certain of their friend's innocence, but are bemused when he intends to accept the charges and refuses their help. Magnum investigates, to find that T.C. trip to the tanker was to collect and bring home a man who once saved T.C.'s life in Vietnam, a deserter who is now a supposedly reformed drug addict, who was calling in an old debt to be flown back in to U.S. territory...

A perky woman hires Magnum to protect 'Norman', who is facing kidnap unless she pays a ransom; but the case has some unexpected turns when Thomas finds that her uncle is an old Vietnam comrade who is against him being hired, and that Norman is none other than a prized race-horse...

Magnum is surprised when a beautiful English woman spurns his advances - much to the amusement of T.C. and Rick - instead preferring Higgins. Thomas is certain that the woman is feigning interest in Higgins only to somehow use him, and plans to uncover the truth, but Higgins sees his doubts as sheer jealousy, and the ever volatile relationship between the two is pushed towards breaking point. Matters aren't helped when Magnum is attacked by a sumo wrestler and a dwarf and, understandably, no-one believes him...

For an upcoming charity auction organised by Higgins and an attractive socialite, to be held on the Estate, Robin Masters "donates" Magnum's services, to provide security over the valuable antiques up for auction at the event. Meanwhile, mainland Private Detective brothers A.J. and Rick Simon have been hired to steal back a Ki'i - a stolen Hawaiian artifact - by it's previous owner, who is in rapidly decreasing health and believes that he has been passed on a curse from which he will die, unless the Ki'i is returned to it's intended location of rest within the Hawaiian islands. But the "cursed" Ki'i seems to spell bad luck and trouble for all who come into possession of it...

The crossover continues on Simon & Simon S02E01 Emeralds Are Not a Girl's Best Friend (II).