Meet Nick and Sid Philips—twelve year old cousins who are about to go on a great adventure. Their fathers, who are elite astronauts, have disappeared on a top-secret mission across the Solar System. Now, the calm-thinking Nick and the wild, rambunctious Sid, who themselves are junior astronaut trainees, are asked to blast into space to find their dads and help them complete the important mission. What Nick and Sid discover on their journey is a mysterious, hidden world filled with never-imagined wonders and dangers. They will encounter scary underground rivers, evil creatures that roll through the jungle, a huge blobby monster, and odd, intelligent beings who just may not be so friendly. Despite the dangers, it's up to Nick and Sid to solve the disappearance of their dads—if the boys can manage to survive at all. Come along on their thrilling space adventure far into the unknown. "The upbeat, charming book... keeps the reader's attention from start to finish.... Bright, pleasant sci-fi for kids."—Kirkus Reviews