In the action-packed mystical novel by Mikhail Seldemeshev, the reader finds himself in Green Stones - a fortress that used to house a prison, surrounded by swamps. Strange rumors and conversations circulated about the prisoners of one cell, none of whom came out of there alive... A very popular personality in St. Petersburg comes here - the writer Georges Kapustin, who decided to write a book about those distant events in the fortress and decided to talk with their eyewitnesses. He meets a doctor who practiced psychiatry and previously served in prison.