Watch The Knocking on the Door Full Movie Free Online 123Movies. The evil Dr Fu-Manchu proves to be a master of disguise as well as villainy in this thrilling episode of the popular adventure serial. Adopting the persona of a long-bearded professor, Fu-Manchu pays a visit to London's Madame Tussauds waxworks. Elsewhere, there's something horribly uncanny going on at a remote country cottage: sleuths Nayland Smith and Petrie leave the capital to investigate.