When Hugo and Ada travel to their friend Dorian's planet for the holidays, Hugo is anxious about being accepted by Dorian's powerful family. But when they arrive on Hydrox, there are more pressing things to worry about, as the planet has become a temporary home for refugee butterflies. Displaced from their home by climate change, the butterflies have been offered sanctuary by Dorian's parents, but they're quickly running out of space. Meanwhile, beneath the seas, a strange creature is wreaking all kinds of havoc . . . Can Hugo, Dorian, and Ada step in before the crisis gets out of control?