Pianist Irka rents a two-room apartment. She sleeps in the small room, and in the large room there is an antique piano. And at night this piano behind the wall begins to sound quietly. Someone presses several keys in turn - the same ones, over and over again. This happens every night, from midnight until dawn. Irka does not dare to get up and open the door. And one day two neighbors, having entered her apartment at night and looking into the second room, instantly find their death there...