Brooklyn, Earth. 1949.

Lily Lupino is going to be an astronaut when she grows up. For now, she'll have to settle for listening to science fiction programs on the radio. But when certified Spacetronaut Kosmo Kidd crash lands his wind-up rocket ship in Lily's kitchen, it's a chance Lily can't pass up

Mistaking Lily for a boy, Kosmo agrees to take her back to his floating treehouse in the stars, but it doesn't take long for the other Spacetronauts to figure out that Lily is a girl. Kosmo has accidentally broken Spacetronaut Rule #1: NO WIMMEN ALOWD

Banished to the far reaches of Outer Outer Space, Lily and Kosmo explore exotic alien worlds, meet a menagerie of colorful creatures, and tangle with the vilest villain in space, The Mean-Man of Morgo. But Lily's greatest challenge is proving to her new Spacetronaut peers that a girl from Brooklyn can hold her own among the galaxy's unruliest rascals.