The plot of M echoes the fascination with shadowy syndicates and underworld figures that Lang exhibited in earlier films such as the Dr. Mabuse pieces and Spies : When a police dragnet for the child murderer upsets normal criminal activities, the criminals themselves organize and track the suspect down, labeling him, without his being aware of it, with a chalk "M" on the back of his coat.
Mabuse film while introducing some of the principles of editing continuity found in M. Scripted by Thea von Harbou (Lang's second wife), it pits a government agent (Willy Fritsch) against a wheelchair-bound international banker (Rudolph Klein-Rogge) whose spy ring is stealing classified documents, and its fanciful and imaginative approach to the thriller form clearly inspired both Alfred Hitchcock and Thomas Pynchon.