Jeff Randall is on a divorce case for a Fay Sorrensen, and presents her with many photographs of her husband in intimate situations with other women. Mrs. Sorrensen, who is apparently suffering from heart problems, plans to divorce her husband Mr. Sorensen, knowing that he won't be able to keep hold of his business assets in the steel company where he works, as her father founded the company and she is a major shareholder.
Knowing this, Mr. Sorrensen contacts a firm specialising on contract killings on the number 0676750. With Jeff away on business, Marty Hopkirk travels to the Sorrensen's the next day, with the intention of speaking to Mrs. Sorrensen's solicitor with her present. However, before he can get to do so, Fay is electrocuted in her bath upstairs, by a cable threaded through a hole in the wall from a van outside masquerading as an electricity van, operated by Dave Carter.
Later, Marty speaks to four children on the street, who tell him about the cable leading up into the house - an activity seen from above by Mr. Sorrensen. Attempting to blame her death on her weak heart, Sorrensen then tries to cover his tracks by arranging to have Marty killed. A beatnik known as Mr. Hendy hitches a ride with a local club singer known as Happy Lee, then, when she grows tired of his conversation and drops him off half-way, he tries to hitch another lift with Marty outside his house. As Marty turns down any offer of giving the beatnik a lift, Hendy becomes witness to Marty's murder as he is driven down by a black saloon car. The beatnik leaps into the vehicle and wrestles a gun out of the killer's hand, extorting £500 from him in order to keep quiet to the police.
After attending Marty's funeral, Jeff tries to get some sleep, only to be woken at midnight by Marty calling him repeatedly on the telephone. After alternately believing it to be a hoax and his imagination, Jeff manages to sleep until he awakes in a trance at 4am under Marty's influence, and drives down to the cemetery to meet him. There Marty tells Jeff he was murdered, and urges him to continue investigating. Jeff does so, speaking to Sorrensen, Happy Lee and the Beatnik. Finally he tracks down the fake electrician and driver portrayed by actor Dave Carter and he is found murdered by carbon monoxide gas poisoning in his home at 2B Tower House, Fulham Road.
Jeff and Marty decide that the only thing to do is to force Sorrensen to play his hand, so Jeff pays him a visit and Jeff pretends that Marty left him a note informing him of his suspicions of Sorenson before he was killed, and demands £25,000 otherwise he'll go to the police with non-existent statement from Marty. Sorrensen goes straight to his accomplices to arrange Jeff's murder, whereby Marty blows a newspaper on their car windscreen, crashing the car, and leaving them surrounded by pre-arranged policemen. Unfortunately for Marty, he's stayed on the case for so long that daylight has broken, forcing him to walk the Earth for a hundred years, with only Jeff able to see or hear him.