Rainy is part of the first generation of humans born and raised on Mars. To keep them from losing their heritage, teens are set up with pen pals on Earth. Rainy learns a lot from her pen pal, Neptune. Most importantly, she learns that things are not good on Earth; people are suffering the effects of global warming, pollution, pandemics, and other problems. Rainy finds a real connection with Neptune, and as she learns more about how dangerous life is for Neptune and her family, she becomes increasingly desperate to help her get to Mars. But those in power are very selective about which Earth-dwellers are admitted to Mars, and Rainy finds herself up against unimaginable obstacles to save her friend's life.