Thorgal and his family have decided to leave their island forever to try to discover their destiny. But as they sail on the waters they are caught in a storm and then separated. Thorgal ends up failing, with Louve, on a strange island occupied by a poplade of Greek origin. They venerate a mysterious creature called Arachnéa, a princess once betrayed by her father and who is condemned to hiding underground and to devour twice a year of young Ephebs. Thorgal will have to face new obstacles to free his daughter prisoner in the heart of the island.