Harry Wallis was once the partner in the police force of Marty's father, Larry Hopkirk, until Maurice Crabbe killed Larry and disabled Wallis, in revenge for their killing of his brother, the hardened criminal Sidney Crabbe, though Maurice is also left severely disabled by the incident. Marty's tuition from Wyvern concludes, and he is then able to enter Limbo, but there he realises that its attractions are only superficial. Now that Wallis is approaching the end of his life, to salve his remorse he hires Jeff and Jeannie to locate Maurice Crabbe so that he can give him some of his savings to pay for his care.

In the week before private detective Marty Hopkirk's wedding to waitress Jeannie Hurst, he and his partner, Jeff Randall, get a job from famous artist Gordon Stylus to watch over his wife, as he fears for her safety. In the course of the assignment, Marty is killed, and the grieving Jeff and Jeannie must investigate how he died, which then endangers their lives. Fortunately Jeff begins to get help from Marty's ghost, which only he can see. Marty fails to get back to his grave in time and is cursed to walk the earth for the duration of Jeff Randall's life, visible only to him...

The enigmatically beautiful Lauren Dee hires Jeff to investigate the disappearance of her husband somewhere in rural England, but it proves to be just a ploy to entice Jeff and Marty into the grip of a village that Time has bypassed since the Middle Ages. Wyvern realises that the only way to save Marty is to enlist the help of Jeannie.

Jeannie joins the private detective agency, and investigates the repeated disappearance of money from the till of a local casino. Meanwhile, Jeff goes to a private psychiatric clinic run by Dr Lawyer, to try to get over Marty's death and rid himself of the ghostly apparitions. Marty gets tutorials in being a ghost and doing impersonations from his mentor Wyvern. After Jeannie solves the case at the casino, the detective agency's offices are broken into, and the trail leads Jeannie back to Jeff at the clinic.

Douglas Milton is writing a book revealing matters relating to security and terrorism, that many authorities and organisations would rather be kept secret, which makes him a prime assassin's target. Jeff and Jeannie get an assignment to protect him from harm until he makes the revelations public at a prestigious international conference.

When Jeannie senses that her nephew, Daniel, is unhappy at his boarding school, she quizzes him about it, and he lets on that he thinks a teacher was murdered. Jeff and Jeannie get jobs there as teacher and nurse, to investigate, and find that the headteacher is exerting a sinister influence on the boys.

Jeff and Jeannie are hired to investigate goings on at a hotel that is supposed to be haunted. Jeff has a disbelief in ghosts until Marty re-appears and gives Jeff back his memories of Marty being a ghost.

Jeff's ex-fiancee Freya Cargill asks him to re-open investigations into the death of her Egyptologist father. Jeff and Jeannie head for the museum where he worked, and meet some of the strange staff who work there.

Jeff and Jeannie are hired to investigate the apparent suicide of a young gay man on the remote island of Strait Isle in Scotland, the inhabitants of which are starting to show some bizarre character traits. Their enquiries start at the brewery where the man worked.

At the request of Bulstrode and Lacey, Jeff and Jeannie pose as doctors to investigate activities at a secret underground pain-research laboratory.

Jeff and Jeannie are hired to investigate what is happening at the home of an eccentric family. But so are their arch-rivals Marshall & Snellgrove, another firm of private detectives, who use the offices below theirs.

When the baby of their secretary Felia is kidnapped by the sinister Butranekh Cult, Jeff and Jeannie investigate some unpleasant goings on in Latvia.

Jeff and Jeannie investigate an empty department store, where a crook's love of playing games has reached lethal extremes. But Jeff and Marty's relationship has reached such a nadir that Marty is cast adrift in Rhadamanthus-On-Sea.