As a result of traveling along the Mana River, people meet who either need each other or are each other's enemies. It is especially difficult to remain human when a jewel is wedged into such a relationship and affects the person. Gleb Dubovtsev did not believe in the possibility of the existence of something unusual and irrational in our days. It could not even occur to him that fate had already prepared a meeting with this irrational one. How the situation “servant - mantis - master” is presented in this novel and what conclusion everyone needs to draw can be drawn by reading two books of this novel.