The novel is set in London in 1886 and follows the life of Mr. Verloc, a secret agent. Verloc is also a businessman who owns a shop which sells pornographic material, contraceptives, and bric-a-brac. He lives with his wife Winnie, his mother-in-law, and his brother-in-law, Stevie.
The novel begins in Verloc's home, as he and his wife discuss the trivialities of everyday life, which introduces the reader to Verloc's family. Soon after, Verloc leaves to meet Mr. Vladimir, First Secretary in the embassy of a foreign country (implied to be Russia). Although a member of an anarchist cell, Verloc is also secretly employed by Vladimir as an agent provocateur. Vladimir informs Verloc that he is far from an exemplary model of a secret agent and, in order to redeem himself, must carry out an operation - the destruction of Greenwich Observatory by a bomb explosion. Verloc later meets with his friends, who discuss politics and law, and the notion of a communist revolution. Unbeknownst to the group, Stevie, Verloc's brother-in-law, overhears the conversation, which greatly disturbs him.