Agatha Christie : The Unexpected Guest

When a stranger runs his car into a ditch in dense fog near the South Wales coast, and makes his way to an isolated house, he discovers a woman standing over the dead body of her wheelchair-bound husband, a gun in her hand. She admits to murder, and the unexpected guest offers to help her concoct a cover story. But is it possible that Laura Warwick did not commit the murder after all ? And if so, who is she shielding ? The house seems full of possible suspects...