Cavanagh has inherited responsibility for a Muslim holy relic, the Slipper of the Prophet after the man who uncovered it, Prof. Deeping, is murdered. Now a league of Muslim assassins called the Hashishin, and a celebrated American cracksman named Earl Dexter fight for possession of the slipper. The Hashishin leave a trail of severed hands and dead men in their path as they and Dexter pursue the slipper, with Cavanagh and Scotland Yard"s Inspector Bristol always one step behind.