Billia befriends Antonio (nicknamed Tottoi) after Tottoi and his father relocate to Sardinia following the death of Tottoi's mother. As Tottoi adjusts to his new life, Billia becomes part of his social circle in Sardinia. Billia joins Tottoi in the central adventure sparked by Tottoi's discovery of a monk seal—an animal species believed extinct—and participates alongside him in the ensuing events.