The Lodger (1926)

Hitchcock's third feature is the first true 'Hitchcock' film, and was called "the finest British production ever made" by the trade journal Bioscope. His first suspense thriller, it's about a mysterious lodger who might also be a serial killer terrorising fog-shrouded London - and, much as he would later do with Cary Grant in Suspicion (1941), Hitchcock cannily cast matinee idol Ivor Novello in the title role and challenged his audience to think the worst of him. Visually, it was extraordinarily imaginative for the time, most notably in the scene in which Hitchcock installed a glass floor so that he could show the lodger pacing up and down in his room from below, as though overheard by his landlady.