Prominent attorney Walter Pidgeon takes a murder case pro bono, wins an acquittal and discovers that his client (Keefe Braselle) was not only guilty but part of an extortion ring reaching to the highest eschelons of the city. Panged by his own complicity, he undertakes an investigation, stumbles onto the identity of the "unknown man" who heads the syndicate, and murders him.<br /><br />The ironies engage when Braselle is charged with this second murder and Pidgeon must defend him by pointing to the existence of another "unknown man" -- himself. Though somewhat short of urban grit and long on rhetoric, the Unknown Man belongs to the noir cycle less by style or structure than by its acknowledgement of the pervasive corruption of American municipal politics that came to light in the postwar years.