The Little Walls

Winston Graham's The Little Walls won the first Crossed Red Herring Award, now known as the Gold Dagger Award. Why did he do it?The purpose of Philip Turner's journey to Amsterdam is to investigate the apparent suicide of his bother Grevil. He has not seen him for several years. His enquiries lead him from Holland to Capri in search of a mysterious girl to whom Grevil had written a cryptic farewell note.
What part does the shadowy Jack Buckingham play? Why can he not be found? Martin Coxon is the only man who has ever known Buckingham well, but it is the girl who seems to have all the answers if she can be persuaded to talk.