From a train window, crane-driver Michael Redgrave thinks he sees a woman being strangled. What follows is an unusual and effective story involving a magician, his assistant wife and a subtle interplay of illusion and murder. Refreshingly directed by the overlooked Herbert Mason, and well performed throughout (particularly Redgrave and Sally Gray), this small gem benefits greatly from its varied and credible London backgrounds, including music halls (including magic shows), mundane work places not normally seen in British films of the period, and construction work on Waterloo Bridge, under which the National Film Theatre is situated (which is where I last saw this film).