I felt echoes of "The Lady Vanishes" while watching this story unfold as we follow “Ruth” (Jeanne Crain) on a cruise liner. She set sail with her new husband, “John,” but he’s disappeared. It's not just a disappearance; there isn't any sign of him anywhere. The Captain (Willis Bouchey) and the ship’s doctor "Manning" (Michael Rennie) seemed skeptical about her mental state – and as she grew increasingly agitated and desperate, many people started to believe that the man never existed at all! However, it slowly becomes clear that this is a carefully crafted game of deception with someone manipulating the woman for her money. Fortunately, the doctor appears to recognize some sense in her actions, and perhaps he can assist her in stopping them from driving her insane – or even pushing her overboard! Crain carries the film well; she portrays the transition between clarity and madness quite effectively. While Rennie might be a bit bland, it’s still a pretty captivating and puzzling seafaring mystery with a mournful foghorn sounding throughout like a funeral chime!

Source on TMDB