This is a black and white movie I watched on You Tube. A group of men are setting off bombs in London. However a secret agent (John Loder) is on to them. However they discover him, and have to be more careful with how they transport the bombs. The bomber, Karl Verloc (Oskar Homolka) sends the bomb in a movie case with his wife's (Silvia Sidney) younger brother (Desmond Tester). However the boy takes longer, due to his own lallygagging and also due to a parade that gets in the way. He is forced to take a bus, and the time slowly trickles away. The inevitable happens, and the bus is blown up. The wife, older sister realizes what has happened, and how. When her husband, now a murderer, approaches her she stabs him.
I love looking for Alfred Hitchcock amongst the extras and this film doesn't disappoint. The part that isn't believable is the relationship that develops between Mrs. Verloc and the secret agent.