Footsteps in the Fog (1955)

To his Victorian London friends, Stephen Lowry is a heartbroken widower. Only his housemaid Lily knows that far from dying of gastroenteritis, his wife was slowly poisoned by her husband--information she is happy to use to improve her position in the household and to make sure she stays close to Stephen. As his own prospects improve with a business partnership and a romance more of his own class, Stephen decides that Lily must go. Unfortunately for him, his first attempt gives her even more of a hold over him.