Secret Agent Ted Spencer goes undercover
as a grocer to expose a band of spies operating out of a London
movie theater. The theater owner, Verloc, asks Stevie, the
young brother of his innocent wife, to deliver a package of films,
which actually contains a bomb.
When Stevie is delayed, he is killed
when the bomb explodes in a crowded bus. Mrs. Verloc avenges
her brother's death by killing her husband, but her guilt is hidden
when the movie theater itself is blown up by another saboteur.