While London Sleeps is a 1926 Warner Bros. film about a police-dog, Rinty, who helps Scotland Yard defeat a dangerous criminal organisation known as the Mediterranean Brotherhood that operates out of the Limehouse district of London.

While the film has no audible dialog, it was released with a synchronized musical score with sound effects using the Vitaphone sound-on-disc process.

[4] George Kotsonaros only appeared in two horror films, this one and The Wizard (1927), and he played a beast-man in both movies.

[4] Inspector Burke of Scotland Yard concentrates all his forces on the capture of London Letter, a notorious criminal leader in the Limehouse district who possesses both Rinty, a splendid dog, and a man-beast monster called The Monk who ravages and kills at his master's command.

Burke and his men wound London Letter while on his trail, and Rinty finds him dying.