When Metropolis director Fritz Lang announced that his first sound film would be about a child killer, he was initially denied studio space because the production head assumed the film would depict Nazis. The studio relented after receiving an outline of the plot, but in the end, Lang assembled a damning criticism of 1931's Germany told through its criminal underground. M is a dark, deeply disturbing, must-see masterwork that bridges the gap between German Expressionism and film noir, and it seethes with hatred toward both humanity and the crumbling Weimar Republic that allowed the Nazi Party to march in and pick up the pieces. Peter Lorre stars as the child killer, but remains an unknown factor in the early part of the film; we don't see him, but we hear him whistling Grieg's "In the Hall of the Mountain King" every time he takes a child. As the police crack down on Berlin to trap the killer, the criminals organize their own far more effective manhunt. The Webster Film Series screens M tonight at 7:30 p.m. at Webster University's Moore Auditorium (470 East Lockwood Avenue; 314-968-7487 or www.webster.edu/film-series). Tickets are $4 to $6.