Visiting a lonely hamlet perched on a cliff above the English coast, forensic detective Dr. John Thorndyke goes for a walk on the long, deserted beach. In the sand he finds two sets of footprints, made some hours apart. They lead to a crime scene. A man has been found stabbed through the heart, his body thrown from the cliffs above. The local police are on the hunt for clues, but Thorndyke is certain the killer's identity can be determined from the footprints in the sand. With the tide coming in, he has only a few hours to catch his man.