Chicago in the twilight of streetcars - A prominent investment broker approaches private investigator Frank Lydecker to discourage a blackmailer threatening to expose a wartime encounter with a teenage girl. The blackmailer is presumed to be a soldier from the broker's infantry squad. When the suspected blackmailer is murdered, Lydecker clears him of blackmail and agrees to find the remaining soldiers from the broker's wartime squad. Lydecker joins police detective Andrew Brooke and the two lifelong friends soon uncover a trail of deception and murder that leads to a shadowy contract assassin and a shocking revelation.