The narrative opens in a shabby Soho shop kept by Mr Verloc, a nominally obscure merchant who secretly works as a spy for a foreign embassy. He lives with his wife Winnie, her mother, and her intellectually disabled brother Stevie. Summoned to the embassy, Verloc is berated by the haughty First Secretary, Mr Vladimir, who declares that Verloc's long-standing reports are useless and demands a genuine, startling act of terrorism to shake the complacency of the British middle classes. Vladimir suggests blowing up the Greenwich Observatory as an abstract attack on science.
Returning home in deep dismay, Verloc is surrounded by his associates—a group of revolutionaries including the senile terrorist Karl Yundt, the aging optimist Michaelis, and the cynical ex-medical student Ossipon. Although they espouse radical doctrines, Verloc finds them profoundly futile. Meanwhile, the authorities are stirred into action.
The Assistant Commissioner of Police, dissatisfied with the routine methods of his Chief Inspector Heat, takes up the investigation personally after a catastrophic explosion in Greenwich Park leaves an unknown anarchist blown to pieces. Inspector Heat discovers a label inside the dead man's coat bearing the address of Verloc's shop. The Assistant Commissioner, seeking to protect the vulnerable Michaelis from arbitrary arrest and realizing that Verloc is entangled with foreign embassies, goes directly to a high-ranking Cabinet Minister to secure a free hand. Through a series of quiet manoeuvres, Verloc's domestic life begins to unravel as his wife's mother departs for an almshouse, and Verloc takes Stevie into the country, setting the stage for an inevitable tragedy.
