The book takes place in 1900. It's a leap year, people don't like it; it is believed to bring bad luck. According to the calendar, February 29 is the day of St. Cassian - it is called Kasyanov all year round. Lykov, at the request of Finance Minister Witte, goes to Kyiv. There, Witte's son-in-law Mikhail Mering got involved in risky scams. He is involved in home construction and has accumulated many loans. But there is a crisis in construction, and Mering faces bankruptcy. Trying to deceive creditors, he cheats with collaterals. The bank's appraiser found out about this and wrote to the swindler's father-in-law. Alarmed Witte asks Lykov to figure out what is happening there. The detective came to Kyiv and learned that the appraiser had disappeared without a trace...