The adventures of the staff of the Institute of Experimental History continue!And this time they will meet face to face with an extremely unexpected opponent … It would seem that the routine operation to find the legendary artifact of the XII century - a mechanical head that gave the rulers wise advice could turn out? The artifact turns out not to be an artifact, but quite a living representative of a race of snake-like intelligent beings divided into winged "angels" and underground "demons" hostile to each other. Even worse, he is actively supported by the young and mysterious prophet Son of Perdition, in which the staff of the Institute recognize with astonishment Fedunya Kochedyzhnik, recklessly rescued by Fox and Kamdil from Chersonesos prison …. And when the enmity of snake-like "angels" and "demons" is connected with the still frantic Bernard of Clervos, his longtime enemy - the cunning confessor of the King of France Suger and trying to take over France Byzantine Princess Nicotea - the situation completely turns into a tangle of continuous problems.