The discovery that Professor Tikhomirov came to after two years of hard work promised to be a sensation - he finally figured out why the frescoes of Andrei Rublev, which once adorned the Spassky Cathedral of the Andronikov Monastery, were destroyed. The scientist anticipated how his book would produce the effect of a bomb exploding, but he felt that he had gotten involved in a risky business that threatened his life. And the premonition did not deceive - Tikhomirov was killed, and the manuscript of his book disappeared... Shortly before his death, the historian managed to convey a call for help and leave three clues that would help solve the mystery. They fell into the hands of journalist Margo Lenskaya and deacon Andrei Bersenev. Fascinated by the professor’s mystery, they soon realized: we are talking about an artifact that could change the entire history of mankind...