Famous astronomer Dr. Arnot gives Nancy, Bess, and George a star-studded planetarium show and promises to let them gaze at the night sky with his famous telescope, the Starship 5000, but the telescope goes missing. It's up to the Clue Crew to investigate the suspects and track down the telescope snatcher.

After watching a movie about aliens during a sleepover, budding scientist Art Smart and his friends spot what looks like a purple space ship headed their way. Each chapter ends with facts about such topics as UFOs and space exploration.