Auzou Book for the unicorn master tome 7 the seahorse plot

Captured by the sea horses of Ville-Méduse, Aëlig, Illana, and Hiyama manage to escape death thanks to the help of a mysterious masked sea horse. Setting out to find Kalyane, who is held captive in this underwater city, they discover that the Hi and their Guide are hiding more than one secret... Will they finally manage to defeat the nameless man and return home?