1913 War is already on the horizon. Riga plants and factories carry out military orders, every figure and detail is of great importance for the Evidentzburo intelligence officers. But the “observation squad” of Russian counterintelligence in Riga is on guard. Counterintelligence officers become aware that the enemy is being supplied with information by a person associated with the Motor plant, for a banal reason - he is being blackmailed. Who is this man? What terrible crime did he commit in the past? How did the Evidenzburo become aware of him? The situation is exactly like the saying “go there, I don’t know where, bring that, I don’t know what.” But the former policeman, and now a counterintelligence agent nicknamed La Bruyère, if he takes a trail, he follows it to the end!..