The book is set in a geological era that scientists call the Paleocene... For many centuries, the world was ruled by terrible lizards. And the animals were forced to live under their power, run away or hide. But then the world changed: they say a piece of the sky fell to the ground. It became cold and hungry, the lizards weakened, got sick and died. But not all. And then the animals saw that they could defeat them. They concluded an Agreement, forgetting enmity with each other, and began to destroy the eggs of the lizards, bringing the end of their dominance closer. The secret battle lasted for many centuries, but there were also those who realized that it was wrong. Several families of animals calling themselves bats left the Treaty to stop the destruction of defenseless young and lead a peaceful life in solitude. The main character of the book is a bat named Dusk, the son of Icaron, the leader of the clan of bats who lived on the island. He was born strange: his membranes (“sails”) were devoid of hair, and his ears were larger than those of his relatives. Already in the first lesson of the gliding jump, he wanted to flap his sails, for which he received a rebuke from his father. In addition, Dusk discovered the ability to see the world in the dark with the help of an echo, and still learned to fly. His parents asked him to hide these abilities from his relatives, because because of his differences from other bats, he is already perceived by everyone as a strange freak. However, his relatives still learn that he can fly, and the wall of misunderstanding becomes even higher. The world of Twilight turned upside down when a huge dying pterosaur flew to the island where Icaron’s colony lived. It was then that Icaron had to tell the young generation of bats both about the Treaty and about the big world. At this time, on the mainland, a representative of primitive predators named Carnassial deals with what he believes is the last nest of lizards, and returns to his native forest to report about this to the leader Patriofelis. And at the same time, he realizes that he no longer wants to eat roots, carrion and insects, having fallen in love with the eggs and tender meat of baby lizards. He invites Patriofelis to start hunting other animals, but for this he is expelled from the clan. However, he finds like-minded people and begins to lead his own life as a predator. After the attack by the Predatory Tooth, the bat clan, having lost some of its relatives, moves to the mainland, where it begins a difficult battle for survival. The world after the lizards turns out to be an overpopulated place, and the former ties of brotherhood of lizard hunters are already forgotten in the light of the new realities of life. New dangers also appear, among which the Predatortooth clan turns out to be far from the most terrible. The bat clan has to face a lack of understanding of their ideas, hostility, and outright meanness that other animals committed for the sake of their own survival. Finding a new home becomes difficult, and the Twilight bat with its ability to fly and see in the dark using echo vision provides them with considerable help.