Yegor is in trouble. He borrowed money to produce young talents, but those young talents, after using him, left for another music producer. Now Yegor must either return the money to the glamorous gangster Maximilian by the end of the week or present him with a new talented star — otherwise, he’s finished. Realizing that in such a short time he will find neither the money nor a star, Yegor flees Moscow “wherever his eyes lead him” and ends up in a backwater town called Glukhomanye. There, through deception, he gains access to a floating pier belonging to a fishery inspection officer named Stepanych, where he plans to lie low while he figures out what to do next.

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.

Olga Barkovskaya helps investigator Kartashova in the case of the kidnapping of lawyer Gennady Sinitsyn, combined with the murder of Gennady's wife Natalia. The criminal sends strange messages consisting of sequences of perfect numbers to the kidnapped man's brother, Judge Semyon Sinitsyn. Each message gives Olga a new clue and brings her closer to catching the criminal, and at the same time reveals terrible secrets from Gennady's past. Kartashova finds it suspicious that the kidnapper is helping to find himself. He is clearly playing a game with the police, the purpose of which only Olga can understand.

Businessman Sergei Andronov and his housekeeper were shot dead in their apartment. At the same time, Andronov's younger brother, 35—year-old Andrey, an autistic and brilliant mathematician, was in one of the rooms of the apartment and may have seen the killer. Olga Barkovskaya helps the investigation, with whom Andrey communicates through mathematical formulas. Andrei himself, the wife of the murdered Albin, a former friend Ilya Riman, and the husband of the murdered housekeeper Stukalov fall under suspicion.

The famous mathematician Lungin was murdered in his hotel room, and an expensive diamond was stolen from his safe. The day before, a tipsy Lungin let slip to the students of mathematics professor Olga Barkovskaya that the safe code opens with ten digits associated with Pythagoras. Senior investigator Svetlana Kartashova has four students under suspicion, and each of them is pointed out by one or another evidence. But Olga, after analyzing the numbers of the code, finds a thread that will lead her to the real killer.

Olga Barkovskaya comes to the defense of her friend, Daria Novikova, who is accused of murdering her husband Anton. But she will be able to find the real killer only by deciphering the message that Anton hid in the text of his book using the Caesar cipher. Olga finds the keys to solving the cipher in the Novikov family history. Revealing the unsightly secrets from Anton's past one by one, Olga gradually gets closer to the most terrible secret that caused Anton's death.

"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.