The countess told him in the prologue that the arsonist/witch had caused the fire and that he had to look for that person for the countess... idk if Caidel actually hated the arsonist (before knowing it was Eleanor), but if he did (and the last panel says he did) then... fuck...
Now I really wonder about Eleanor's life. How did she become "immortal"? And how did she survive in the forest on her own, when there were monsters around? She was around 10 when her teacher died, right?