Ippolit Kalinkin is a former swindler - handsome, smart, mustache. Now he has chosen a new profession for himself - a private detective. Many years of communication with St. Petersburg criminals of various stripes helped Ippolit create a card index. It contains information that allows Kalinkin to catch the most cunning and dangerous attackers. One morning, an old man appears under the windows of Ippolit Kalinkin’s apartment and begins to sing in the most vile voice. This old man seemed not only strange to Hippolytus, but also familiar. Kalinkin is trying to find out who this old man is. Having found out this, he is horrified.