Jack and the Jarl's Plea

After the happiest summer he could remember, Jack is suddenly summoned to heal the Jarl of Cork, an important ally of the king. If Jack can't find a way to help him, war would consume all southern Ireland.
But Jack is reluctant to get involved because he doesn't know what is causing the illness. And worse-much worse-the Jarl is a Dane, just like the ones Jack's father had fought against for so long.
Will Jack help an enemy to help his country? Will he listen to the Jarl's plea?