Synopsis by Hal Erickson
The title character in this Vitagraph five-reeler is a prominent but irresponsible Parisian patron of the arts, played by Robert Edeson. To finance his art collection, Mortmain borrows heavily from his best friend, banker Gordon Russell (Donald Hall). The banker is averse to calling in his loans but changes his mind when he learns that his ward Belle (Muriel Ostriche) is in love with Mortmain. Since Russell himself has long had designs on Belle, he now feels that the time is ripe to cut off Mortmain's cash flow, assuming that the girl would no longer be interested in a bankrupt boulevardier. Shortly afterward, Russell is found murdered, and the evidence points to Belle's brother Tom (James Morrison). Meanwhile, Mortmain seriously injures his hand in an accident, necessitating emergency surgery. While under the ether, Mortmain imagines that Tom's hand has been grafted onto his -- and that it is Mortmain's fingerprints, and not Tom's, that are found on the murder weapon. The nightmare ends for both Mortmain and Tom when the actual murderer finally steps forward. One suspects that Mortmain was based on one of the one-act plays frequently staged at France's Theatre du Grand Guignol.