During the celebration of the dean's anniversary, mathematician Olga Barkovskaya finds the culprit of the celebration murdered. Next to the body is a card from an unknown game, very similar to the one that was thrown to Olga the day before. It seems that Barkovskaya is being invited again to solve a mathematical puzzle, and a human life is at stake.
"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.
