Ms. Verloc (Sidney) discovers that her husband, Karl (Homolka), a London cinema owner, is a terrorist agent. Meanwhile, a Scotland Yard undercover detective (Loder) who has been on the trail of Karl's attacks investigates a plot to set off a bomb in London, but complications arise when the detective's cover is blown.
Not to be confused with Hitchcock's later 1942 film Saboteur. For that matter, the novel this film is loosely based on, Joseph Conrad's The Secret Agent, should not be confused with Hitchcock's film Secret Agent, also released in 1936, but based on a story by W. Somerset Maugham.
This film features examples of:
- Big Blackout: The film begins with London going dark after losing all of its electricity, as it's revealed later, because sand was put in the boilers of London's electricity grid as an act of sabotage.
- Bomb-Throwing Anarchists: The terrorist gang, who resort to a planned series of attacks in London, though whether they are actually anarchists is unknown since their exact motives are not made clear.
- Even Evil Has Standards: Karl Verloc might accept to deliver bombs for a terrorist gang, but after they ask him to place a bomb at the Piccadilly Circus station, he objects that he is not comfortable with any act that would cause the loss of life (though that doesn't stop him from accepting the task, perhaps because at this point he can't).
- Infant Immortality: Shockingly averted. Karl asks Stevie, his wife's little brother, to deliver a film canister to the cloak room under Piccadilly Circus, but what Stevie doesn't know is that he's actually carrying the time bomb the terrorists asked Karl to carry. Stevie is delayed by several events, and the bomb explodes while Stevie is aboard a bus.
- Never My Fault: Verloc blames Scotland Yard and Spencer for Stevie's death rather than himself, saying that they were the ones who prevented him from carrying out the bomb delivery himself.
- Only in It for the Money: It is implied that Karl is with the terrorists not for sharing the same beliefs but because they pay him a pretty penny — after the London blackout affects the Verlocs' cinema and people demand their money back, Karl assuredly instructs his wife to return the money to the customers, despite her protests, because he has "some money coming in."
- Ruritania: The gang of terrorists hail from an unnamed European country.