Jeff Randall and Marty Hopkirk are best friends and business partners in a small London private investigative office.
The partnership seemingly ends when Marty is killed in a hit-and-run accident in front of his home, but Marty's ghost returns, visible only to Jeff, to track down his murderer.
They succeed in trapping Marty's killer, but in the process Marty falls victim to an ancient curse: "Cursed be the ghost who dares to stay and face the awful light of day / Ye shall not to the grave return until a hundred years be gone."
Marty notices something unusual at a funeral near his grave. When Jeff "accidentally" (with Marty's help) stumbles upon the couple who were at the funeral, he understands why Marty was suspicious: evidence points to murder; plus, there are two people claiming to be the dead woman's brother.