Hugo is spending the holidays on his friend Dorian's home planet, Hydrox. Although thrilled at the invitation, Hugo is still astonished that Duke Dorian could possibly want to be friends with an android watchmaker like him. But when the pair land on Hydrox along with their friend Ada, they soon discover that there are much bigger problems afoot.

A race of butterflies from a neighbouring star system have evacuated their now-uninhabitable planet, and Hydrox is struggling to find space for the growing number of refugees. Meanwhile, deep in the seas beneath Dorian's home, a strange creature is on a path of destruction ... Can the unlikely trio step in before the crisis gets out of control? Dive into a strange new world in this truly imaginative companion to The Starlight Watchmaker.