Major Hariev, of the State Security Service, discovers that the spy centre codenamed Citadel receives coded letters. Some time later, the Bulgarian agent in the West reports that the spy has a subscription to a French women’s magazine. State Security officers track down a beautician who received the magazine and delivers it to Ivan Bolyarski, director of an important state department. Hariev follows Bolyarski to a meeting with the Hawk, his associate in a military unit. The Hawk agrees to provide the requested information for an exorbitant sum of money. Hariev encounters the Hawk and kills him in a fight. Bolyarski is arrested. Major Hariev is placed in his cell. In a moment of demoralisation, the agent reveals the secrets of Citadel to Hariev. Hariev must go to Citadel, passing himself off as the Hawk. He takes a leap into the dark, not knowing if he will ever return to his wife and child.