Released in the U.S. as The Woman Alone, this Alfred Hitchcock film starts with movie theater owner Karl Verloc (Oskar Homolka) shutting down the power in London before working with a group of terrorists to leave bombs all over the city. Detective Sergeant Ted Spencer (John Loder) is working undercover to catch him, posing as a grocery store owner while starting to fall for the man’s wife, played by Sylvia Sidney.

The machinations of the terrorists lead to her brother Stevie (Desmond Tester) being killed, and a depressed Verloc literally walks into a knife that his wife is holding, ending his life. Spencer tries to keep her from confessing to the murder, and when the final bomb explodes, destroying Verloc’s body, she is able to get away with it. 

This was loosely based on Joseph Conrad’s The Secret Agent, a story about a woman who learns that her husband is a terrorist. As Hitchcock had already made another movie called Secret Agent. When this was remade in 1959 for the Canadian TV series Startime, Homolka reprised the same role.

When the bus driver remarks in Inglorious Basterds that  “You can’t bring that on here. It’s flammable,” it comes from this.

In one of his interviews with François Truffaut, Hitchcock claimed he was wrong to shoot the scene where Stevie dies, because the character received too much sympathy and “the public was resentful”. Truffaut commented that having a child die in a movie is a “ticklish matter” and an “an abuse of cinematic power.”

You can watch this on YouTube.