An unknown weed rapidly wraps Earth in its tentacles. People who get near the plant go mad. The very Thicket itself generates terrible monsters made from the living organisms it kills. Suddenly it turns out that only people with Down syndrome can withstand the destructive nature of this weed. The Institute of Cosmic Infections assembles a group of travelers for a march to the center of the plant-parasite. Among them, Kostya stands out especially. It is he who must reach the central root and inject a chemical that can destroy the Thicket. But at the end of his journey, Kostya learns something that will change the life of humanity forever…