Like a brand, the letter M has made its mark on film history with its disturbing theme having lost none of its impact or relevance. Sinister, dark and foreboding, M tells the story of Hans Beckert (Peter Lorre) - child molester and murderer. Tension builds - a child late home, another child missing. Posters reveal the fate of earlier victims and the police seem to have few clues as to the perpetrator of the crimes. Gangsters, beggars and petty criminals, incensed by both the crimes and the police crackdown, track the killer themselves. Cornered, caught and dragged off to face an equally barbaric form of justice, Beckert endures his own personal torment. As with his earlier classics Die Nibelungen and Metropolis, Lang collaborated on the script with his wife, Thea von Harbou, in what was to become his most stark and uncompromising film. Allegedly based on the story of Peter Kürten, the "Monster of Dusseldorf", M remains one of the most chilling serial-killer films ever produced.