The adventures of the employees of the Institute of Experimental History continue! And this time they have to meet face to face with an extremely unexpected enemy... It would seem, what could a routine operation to find a legendary artifact of the 12th century - a mechanical head that gave wise advice to rulers - turn out to be? very many... The artifact turns out to be not an artifact, but a completely living representative of a race of snake-like intelligent creatures, divided into winged “angels” and underground “demons” hostile to each other. What’s even worse is that he is actively supported by the young and mysterious prophet Son of Perdition, in whom the Institute staff are amazed to recognize Fedyunya the Kochedyzhnik, recklessly rescued by the Fox and Kamdil from the Chersonesos prison... And when the still frantic Bernard of Clairvaux joins the enmity of the snake-like “angels” and “demons” , his longtime enemy is the cunning confessor of the King of France Suger and the Byzantine princess Nicothea, who is trying to take over France - the situation completely turns into a tangle of continuous problems...