About the true role and place of parasites in nature, about the parasite as the driving force of evolution. About their influence on the immune system and on the sexual behavior of animals, and perhaps on the need for gender division in general. Symbiosis between parasite and host. About the work and discoveries of scientists, about how to learn to live in the world of parasites, why it is not always necessary to fight them and how a parasite can save our planet.