The Dark Eyes of London by Edgar Wallace

When wealthy Canadian Gordon Stuart vanishes during a night at the theater, he's later found drowned on the Thames Embankment. Inspector Larry Holt senses murder, especially when Stuart's strange will reveals a daughter no one knew existed. As Holt digs deeper into London's dark alleys, he must face a ruthless gang of blind criminals—and a sinister conspiracy involving forged identities, secrets from the past, and a terror that lurks in plain sight.