Private Detective West Barns begins a well earned rest in Nice where he meets Sarah Donald and her friend who are looking after two teen age boys until their millionaire parents arrive. When the boys excitedly accept a few days sailing on a luxury yacht by Shawman its American owner the girls agree to go along, and West although he has an inherent fear of the sea also accepts in order to be near the lovely Sarah. However things go drastically wrong when 12year old peter goes for a swim while the yacht lies at anchor and sees something that he should not have. Now events take a different turn, with all of them fighting for their lives. Leaving West to wish he had stayed at home in North Berwick.