I though this had a little of "The Lady Vanishes" (1938) to it as we follow the adventures of "Ruth" (Jeanne Crain) aboard a cruise liner. She embarked with her new husband "John" but he's gone missing. Not just missing, but there's not a trace of him to be found anywhere. The Captain (Willis Bouchey) and ship's doctor "Manning" (Michael Rennie) are not convinced that she's the full shilling - and as she becomes more and more frantic and desperate most conclude that the man never existed in the first place! Gradually, though, we realise that this is quite a clever cat and mouse game with a man playing the poor woman like a fiddle for her fortune. Luckily the doctor seems to see some sanity in her behaviour and maybe, just maybe, he can help her thwart the plan to drive her mad - or, even, overboard! Crain holds this together well. She manages her voyage between lucidity and madness effectively and though Rennie is maybe just a little too insipid, it's still quite an engaging and intriguing maritime thriller with an haunting fog-horn sounding throughout like a mourning bell!