***SPOILERS*** Drowning his troubles in a bottle of scotch at the British Lake Windermere Yacht Club American writer Mark Kendrick, Alex Nicol, spills his guts out to the person, who for the time being shall remain nameless, he meets there about what a fool he was to get involved with icy blond Carol Forrest, Hillary Brooke. It was Carol who manipulated him into doing what he did for her own selfish and murderous interests. That for him to be a pasty in her plans to off her husband Beverely Forrest, Sidney James, and then be left holding the bag as she checked out on Mark with pianist Vincent Gordon,Paul Carpenter.
This nightmare started of for Mark when he was invited to a party thrown by Carol to help ferry with his motor boat her guests back to shore after it was discovered that the boat that took them there was out of gas. It was later that Mark took the gas-tank in being set up to whack Beverely while on a fishing trip at lake Windermear planned by Carol. What really set Carol off was the discovery that her old man, who knew she only married him for his money, was going to cut her out of his will and thus out of the lifestyle she's been so used to living. Also her step-daughter Andrea, Susan Stephen, saw through her and was also doing everything possible to get her dad Beverely to divorce Carol before she did him him for good.
****SPOILERS**** Not realizing that he was being set up Mark together with Carol and Beverly went out on the lake fishing in pea soup thick fog when by avoiding another boat ended up knocking Beverly off the control or watch booth where he busted up his skull and landed unconscious on the deck below. With his back turned and keeping his eye on the steering wheel Carol pushed the unconscious Beverly overboard where he ends up drowning. With Carol who claimed to be in love with him now dumping Mark for the piano player, whom he detested, he just about had all he could take from her and decided to do the right thing. And with that Mark decides to spill the beans of what he did in him being an accomplice, or better yet pasty, in Beverely's murder of her husband. And the person whom he spilled the beans to, as well as buying him a couple of drinks, is the police detective on the case who's been hounding him all throughout the entire movie Inspt.Maclennan, Alan Wheatley.