Sabotage (1937)

Directed by Alfred Hitchcock

Karl Anton Verloc and his wife own a small cinema in a quiet London suburb where they live seemingly happily. But Mrs. Verloc does not know that her husband has a secret that will affect their relationship and threaten her teenage brother's life.

The seemingly 'random' explosion of a bus (with a teenage boy at the heart of it) shows yet again how films carry around the subconscious fears of their times. In this instance, the fear of sustained aerial bombing of a civilian populace of the upcoming war.