My Late Lamented Friend and Partner

Private eyes Jeff Randall and Marty Hopkirk are gathering information to allow Fay Sorrensen to divorce her cheating husband but he murders her and makes it look like a heart attack. Marty is suspicious but is killed by a hit-and-run driver before he can prove that Sorrensen is a murderer. His white-suited ghost gets Jeff to meet him at his grave in the cemetery and they expose the murderer between them. However, Marty has been out of his grave beyond the dawn and must wander the Earth as a ghost for the next century, though only Jeff can see him.