The shop owner Adolf Verloc, member of an anarchist group and secret agent for a foreign government, is summoned to meet Mr Vladimir, the country’s ambassador, who asks him to carry out a terrorist attack at a famous London landmark. Verloc has misgivings, but Mr Vladimir knows how to make people do what he wants, and when the plan goes wrong, it is Verloc - as well as his young wife, Winnie - who must deal with the consequences.