Two friends separated by the stars. One bottle that brings them together. Moonie, stuck on a moon with only her rock collection, desperately wants a friend. So she launches a message in a bottle into space hoping it finds someone-- anyone --who will write back. Junie, stuck on Mars with her family during a boring vacation, is perfectly content simply studying those around her. But when Moonie's message in a bottle lands in her lap, she can't help but respond. After all, it's what any good Junior Space Explorer would do. When Moonie receives Junie's reply, Moonie is determined to make the most of their correspondence.

But when Moonie's eagerness for friendship clashes with Junie's shyness, their budding friendship is put to the test, forcing the pen pals to consider just how far they're willing to go for one another.