Police Major Igor Grom is known throughout St. Petersburg for his penetrative character and irreconcilable attitude towards criminals of all stripes. But everything changes dramatically with the appearance of a person in the mask of the Plague Doctor. Having declared that his city is "sick with the plague of lawlessness", he takes up "treatment", killing people who, at one time, escaped punishment with the help of money and high status in society. Society is agitated. The police officers are powerless. For the first time, Igor faces difficulties in the investigation, the outcome of which may determine the fate of the whole city.