After spotting a radio signal from space, twins Anthony and Astrid team up with their astronomer grandfather to search for extraterrestrial life. On the way, they learn about space concepts, such as effective rocket design, the effects of gravity on astronauts, and properties of planets in the solar system. When they find an alien on the moon, the adventure really begins! Through this informative and entertaining adventure, readers will increase their space-science knowledge as they solve puzzles to help the story's heroes in their exciting mission.