Mr. Verloc is on his way to a certain foreign embassy, summoned there, to his astonishment and unease, at the unseemly hour of eleven in the morning. Ambling down the street, bulky and stolid, Mr. Verloc does not look very much like the agent provocateur that he is supposed to be. He keeps an obscure and ill-patronized little shop, behind which are quarters for his family. There he often entertains a group of London anarchists from whom he carefully keeps the secret that he is an embassy agent. He grumbles inwardly as he approaches the embassy, thinking how awkward it will be if any of his anarchist friends are to detect him in the act of entering such a place.

His appointment with Mr. Vladimir does nothing to improve his mood. In fact, his discontent deepens almost to a state of terror by the time of his departure. Mr. Verloc allowed himself to get comfortable, if not lazy, in the years since he settled in England as the agent of a foreign power; he never contemplated the possibility that he might lose his job. Now he finds himself being roundly abused and insulted for what First Secretary Vladimir is pleased to call his fatness, his slothfulness, and his general inefficiency. He is even threatened with dismissal if he does not promptly promote some incident to upset English complacency. In short, Mr. Vladimir demands a dynamite outrage within a month and further specifies that it must be directed against some monument of learning and science—preferably the Greenwich Observatory.

Badly shaken, Mr. Verloc makes his way back to his shop in Soho. Rejoining his household in the room behind it, he manages to resume his usual demeanor of stolid reserve. When, soon after, his anarchist friends pay one of their calls, he betrays nothing to them of the frustration and fear that lurks behind his impassivity. He is not so successful with his wife. She is able to keep her own counsel, but she misses very little of what goes on about her.

Younger than her husband, Winnie Verloc married him for security rather than for love. It is not even her own security that she is concerned about but that of her unfortunate brother, whose passionate protector she is, ever since the days of their childhood. Now physically mature, Stevie remains childlike in other ways; he is easily excited and inarticulate, although generally softhearted and trusting. One of the people he trusts most is Mr. Verloc. His sister does a great deal to bring about this state of affairs; his mother, who is also being supported by Mr. Verloc, assists Winnie in impressing upon Stevie the idea that Mr. Verloc is good, that his wishes must be instantly carried out, and that he must be spared the slightest annoyance. Meanwhile, Mr. Verloc serenely goes his own way; insensitive to this anxious maneuvering to keep Stevie in his good graces, he largely ignores his brother-in-law even while tolerating his presence in the Verloc household.

To consolidate her son’s position still further, the mother of Stevie and Winnie decides that before Mr. Verloc can tire of supporting both of his wife’s relatives, she will move to an almshouse. Stevie misses her and begins moping. Seeking a remedy for her brother’s moodiness, Winnie seizes upon what seems to her a happy expedient. The long walks of her husband, mysterious of purpose and destination, give Winnie an idea. Finding the right moment to make her request, she persuades her husband to take Stevie with him. To Winnie’s gratification, this experiment soon becomes an established practice. With things apparently going so well, she sees no reason to object when Mr. Verloc makes a rather unexpected proposal regarding Stevie. Since Stevie is fond of Michaelis, an elderly anarchist who frequently visits the house, why not let the brother spend a few days with Michaelis at his retreat in the country?

Apparently pleased with this development, Stevie leaves to visit Michaelis, and the next few days pass without incident in the Verloc household. Late one afternoon, however, Mr. Verloc comes home from one of his walks more upset than Winnie ever saw him. He withdrew all of their money from the bank, and he mumbles vaguely about the necessity of leaving the country. Winnie tosses her head at this—he will go without her, she declares tartly. Mr. Verloc morosely ignores her wifely urgings that he eat his supper and change his slippers. He does not ignore, however, a distinguished-looking stranger who turns up presently and takes Mr. Verloc away. Winnie fails to recognize this caller as the Assistant Commissioner of London Police.

During their absence, a second stranger arrives. Winnie becomes more and more apprehensive upon learning that he is Chief Inspector Heat. When Heat learns that he was forestalled by his superior, he shows Winnie a cloth label bearing Stevie’s name and address. Recognizing it as an identification tag placed in her brother’s coat, she asks wildly where Heat found it. The return of Mr. Verloc, alone, interrupts their conversation. After Heat takes Mr. Verloc into another room, Winnie tries to overhear what they are saying. Almost mad with grief, she hears her husband tell how he trained Stevie to take part in a bombing attempt upon the Greenwich Observatory. Stevie, however, stumbled in the fog, exploding the bomb prematurely and blowing himself to bits.

After Heat leaves, Winnie faces her husband. White-faced and rigid, she hardly listens to his faltering explanation or his plan to turn state’s evidence on the promise of a lighter penalty. When, exhausted, he finally drops on the couch, she seizes the carving knife and stabs him in the heart. Winnie runs aimlessly out into the dark and stumbles upon Comrade Ossipon, one of her husband’s anarchist associates who has eyed her from time to time with admiration. After promising to help her, he discovers, with consternation, what occurred and that he might be implicated in the affair. Coaxing her onto a boat train, Ossipon waits until it starts to move; then he leaps off. With him, he takes the money that Winnie entrusted to his care.

A week passes. Ossipon does not enjoy his possession of Winnie’s money; he feels heavily burdened by gloom and guilt. The feeling deepens as he reads a newspaper report of the suicide of a female passenger from a cross-channel boat. He is convinced that the last words of the dispatch will always haunt him since he alone knows the truth about Winnie’s death, a deed that the newspaper calls a mystery of madness or of despair.