Kennedy Balfour, ex-RAF in post-war Britain, helps a frightened young woman on a train, but doesn't realise what he's getting into. He only knows that Delia Thomas is beautiful, and terrified of the man following her. Apparently the man, known as 'Swarthyface', is a criminal mastermind and his main target is the girl's father. And if Balfour persists in protecting the girl and her father, then one of them would die ... and that someone might very well be himself.