"The Secret of the Ninth Planet" is an exciting science fiction adventure book written by Donald Wollheim. The action of the novel unfolds in outer space, where a group of brave scientists and travelers sets out on a long journey to the ninth planet. Controversies, mysteries and danger await them at every step, but only a coordinated team will be able to solve the mysteries of space and save the world from the threat. This book not only captivates with its story, but also leaves the reader thinking about the nature of the universe and human curiosity. "The Secret of the Ninth Planet" is a masterpiece of science fiction that will captivate all lovers of space travel and mysteries of the universe.