Jimmie Dale and the Phantom Clue - Frank L. Packard

Jimmie Dale, alias The Gray Seal, alias Smarlinghue, is back in the criminal underworld of New York. He is desperately trying to find the criminal called the Phantom, alias Gentleman Laroque, in order to protect Marie, alias The Tocsin, the love of his life. A fast-paced, adventurous story riddled with aliases, disguises, gunfire and opium dens.

Third book about the adventures of Jimmie Dale. The first two are already available at Librivox. - Summary by Anna Simon