1925. There have been unrest in Western Belarus for four years now, there is a guerrilla war going on, and Soviet intelligence agents are working. And attempts by local residents to defend at least their own faith and church end in brutal suppression.
"Your husband is sleeping with your student" – Olga finds such a note in one of the bouquets that were presented to her in honor of her triumphant speech at the scientific forum. Olga is a mathematician. She can easily figure out who sent this anonymous letter. Except this man is found dead. This is how a dangerous game begins, each move of which is associated with one of the Fibonacci numbers. What do they mean and how are they related to Olga's life? The answer is far in the past. Every mistake will cost the life of someone close to the heroine.