"'I've been to a lot of places - a lot of worlds. But Something or Somebody kept holding me away from this one. I can make a pretty good guess Who, too.'" (p. 41)
To me, the capital letters mean God and the reason would be that Holger, a Chosen hero, should not have personal quests but should hold himself ready for the next Quest and should not be trying to settle down any century soon. However, Alianora makes the opposite interpretation:
"Alianora could make that same guess. If the Powers Holger had bested here had their way, they would never want to see him again." (ibid.)
So she thinks that it is the Adversary who has put obstacles in Holger's path. But could it be both sides for their own contradictory or complementary reasons? The forces of Chaos must be allowed to gain strength again before it is the appointed time for them to be driven back again?
Poul Anderson shows us Valeria Matuchek:
on a field trip for a Master's degree and advising Holger.
He shows us Holger:
visiting the Carolingian universe and wanting to return there;
traveling between universes and receiving advice from Valeria.
Harry Turtledove shows us Holger returning to the Carolingian universe. Thus, Turtledove completes a sequence initiated by Anderson.