What is the main conflict in The Other Wind by Ursula K. Le Guin?

The main narrative of the book concerns itself with the fate of Alder, a humble village sorcerer with the power to mend things by his magic. Every night, Alder is being drawn in his dreams to the low stone wall that separates the lands of the living from the lands of the dead, and there his recently departed wife Lily is calling to him and reaching for him across the wall.