In the packed queue for a popular West End Theatre in 1920s London, the crowd surges forward as the doors open at last... But as they do so, one of their number falls to the ground - a man, stabbed in the back with a stiletto while people jostled for position in the throng. There is nothing in the man's clothes or wallet to identify him, and nothing in his pockets but a revolver... Who is he and who killed him before melting away unseen into the night?

Inspector Alan Grant investigates, and soon is engaged in a breathless manhunt that will lead him from London all the way to the Scottish highlands and back, before the mystery is finally resolved in a way that not even he can anticipate.