As Thorgal pursues the kidnappers of the young Aniel, his eldest son Jolan is about to finally cross the threshold of adolescence. Winner of perilous trials, he must now enter the kingdom of Asgard to bring back a fruit of it from the garden of Idun, the only remedy to save Vylnia, Manthor's mother. To achieve this objective, Manthor has entrusted him with an army. But, can she protect him from the schemes of the perfid Loki? One thing is certain: the young man will come out transcended from the kingdom of the gods...