Private detective Jeff Randall is hired by Fay Sorrensen to get evidence that her husband is cheating. Jeff collects the evidence, but is unavailable to meet with Fay for payment. Partner Marty Hopkirk goes instead, but before he can meet with Fay she dies in the tub. The doctor rules her cause of death to be a heart attack, but Marty thinks otherwise. Before he can convey his suspicions to Jeff he, too, dies, hit by a car as he is crossing the street to go home. Following the funeral, a devestated Jeff finds himself at the cemetery in the middle of the night where he encounters Marty's ghost. Marty has returned to tell Jeff it was not an accident, but murder. Marty can only help Jeff at night because of an ancient curse that says, "Afore the sun shall rise anew each ghost unto his grave must go."
Jeff's argument with ghost Marty is caught on tape by Jean and her sister Jenny. They conclude Jeff needs psychiatric help. Jeff lands in a hospital run by a psychiatrist who uses hypnosis to get patients to willingly hand over their valuables to a robber. Marty must get Jeff out of the hospital before the doctor can "edit the ghost" out of Jeff's mind.
Marty witnesses a murder, but by the time he can convince Jeff to leave his date and investigate, things are not as Marty saw. The man he saw murdered, a government employee named James Howarth, is alive and threatening to call the police on Jeff. Marty knows what saw, but he cannot convince Jeff to investigate because Jeff is afraid of losing his P.I. license -- and because a "ghost expert" friend has convinced Jeff that ghosts live in a world of hallucinations.
A clairvoyant member of a robbery gang knows Marty is around. He uses this knowledge to full advantage, feeding false information to Marty (who, in turn, gives it to Jeff). Jeff gives the bogus information to Inspector Large, clearing the way for the robbers to strike elsewhere. Because Marty knows too much about the robbers, he must be disposed of, so the gang plays on Jean's emotions to get her to cooperate in an exorcism of Marty.
Marty appears on Jeff's desk in the office, but Jeff does not respond. He does not hear or see Marty, nor does he act like he cares that his ghostly partner has suddenly vanished. Worse, Jeff is making advances toward Jean. Marty thinks Jeff is working too hard on his latest case, investigating stock leaks from the Towler Corporation, so he uses a psychiatrist's hypnotized patients to try to reach Jeff. The attempts fail; worse, Jeff kills the Towler Corporation executive who hired him.
Marty's aunt hires Jeff and Jean to escort her to Monte Carlo. She has perfected a "foolproof" mathematical system that allows her to win at roulette. When she arrives, different groups get word of her system and attempt to steal the notebook she carries with her.
Millionaire Kim Wentworth thinks her house, Crake Castle, is haunted, so she hires self-proclaimed "ghost hunter" James McAllister to find the ghost. McAllister (who cannot detect Marty standing next to him) offers Jeff a share of his fee to prove that the "ghost" at the castle is a phony. Jeff takes the job -- then McAllister is murdered.
A woman hires Jeff to find her wealthy missing aunt. The aunt's only hobby was going to a seance once a week. When the woman who hired Jeff is supposedly killed by a drunk driver, Jeff decides to continue looking for the missing woman. He discovers a connection between the seances and a financial consultant, the last person to see the missing aunt.
The estate of bird lover Mrs. Wentworth Howe has been held in trust for ten years, as her will stipulated that her money would not be distributed to surviving family as long as any of the birds in her aviary remained alive. When one of the birds is shot dead, Jeff is hired to investigate if a family member might be getting impatient for their share of the estate. Jeff soon has a bigger problem on his hands as family members gathered at the Howe mansion are murdered.
While in the bathroom Jean hears a noise. She goes to investigate and discovers a man lying on her sofa, making himself at home, claiming to be the reincarnation of her late husband, Marty. Jeff knows this isn't true, but how can he convince Jean, who finds herself believing the man's claims?
A boast about the ability to acquire an unlimited amount of bearer bonds puts con artist Calvin Bream in hot water with a ruthless criminal. In an effort to get himself off the hook, Bream poses as an American looking to hire Jeff as a bodyguard. While Jeff becomes entangled in the bearer bond scheme, which leads to murder, Marty makes an interesting discovery: whenever Bream is drunk, he can see Marty.
Marty finds his headstone knocked over at the cemetery. While investigating, Jeff is hit with a shovel and knocked out by a man dressed in 18th century garb. His head injury is treated by the owner of the mansion located next to the cemetery, a man with an agoraphobic son living in the basement. When the son is kidnapped, Jeff finds a connection to the strangely-dressed man who hit him.
Jeff is hired to go to Glasgow, pick up an item worth £10,000, and return it to London. He is against taking the job, especially because two rival criminal bosses are involved. He becomes more suspicious when the "item" turns out to be the blonde girlfriend of one of the criminals. When they arrive in London she vanishes, leaving Jeff hunted by both criminals who think he double-crossed them.
Just at a time when Jeff could use some money an old friend shows up with a money-making proposition. Not so much money "making" as money "taking": he suggests to Jeff that they steal old notes that are en route to the incinerator. Jeff watches from a distance to see if his friend shows up and ends up in jail charged with the crime when the police prove he was in the vicinity and his alibi falls through. Worse, he refuses to tell Marty what happened, leaving Marty unable to help.
-- I'll Take You Home Again, Kathleen
Jeff breaks his legs on a case. Confined to his hospital bed, he has to listen to Marty tell about the agency's "greatest case." While Jeff had been away in Scotland, Marty became entangled in a spy case where he was tricked into stealing a list of MI5 agents for a foreign agent.
Just before taking a simple assignment -- collect invitations from family members for a private 80th birthday party for Joshua Cracken at Cracken's estate -- Jeff and Marty have an argument during which Jeff tells Marty to stop haunting him. Once the guests at the Cracken birthday party begin mysteriously dying, Jeff wonders if he should have run Marty off so quickly.
Eric Jansen breaks out of a prison psychiatric unit with revenge on his mind. The object of his vengeance is Marty Hopkirk, the man responsible for his imprisonment. When he discovers Marty is dead, he picks an alternate target for his rage: Jean, Marty's widow.
When Jeff arrives home at 8:00 a.m. he finds a nun sitting at his dining table. She says she needs to hire him to investigate a man who has stolen from her convent. When the "convent" turns out to be an electronics company, Jeff discovers the nun is part of an elaborate set-up to make him the lead suspect in the theft of company documents.