Volume 2 of collected works. Three researchers, testing the technology of interdimensional travel, find themselves among the Stone Age jungle, where they discover a civilization that has learned not to subjugate nature, but to live in harmony with it. Nature gives the people of biological civilization everything: food, clothing, shelter. Everything here is subordinated to harmony, each person knows his place in society. But the well-being of civilization depends on the health of biological computers that store the experience of the past and, on its basis, manage life in this society. However, as a result of a natural disaster - a supernova explosion - biological machines go crazy. As a result, biological civilization dies.