About the book: 1997 / The Return to the Future cycle consisted of the novels "The Mystery of Zero" and "Don Quixotes of the Universe." The novel "The Mystery" zero" is dedicated to proving that stellar flight is possible at sub-light speed, when the flow of time on a starship slows down according to Einstein's theory, into which the concept of "mass ratio" should be introduced. The second novel, “Don Quixotes of the Universe,” is about the stay of astronauts on a twin planet during the Middle Ages. The hypothetical novels of the oldest Soviet science fiction writer pose moral problems and suggest possible scientific solutions. Drawings by A.M. Eremina.