The Wrong Side of Magic — Janette Rallison

Hudson Brown stopped believing in magic long ago. That is, until the day he is whisked away to the magical land of Logos by a curious compass given to him by his off-beat neighbor, Charlotte.

Hudson discovers that Logos is a land ruled by words, thoughts, and memories. A fairy might ferry you across the river for the price of one memory. But be sure to look out for snarky unicorns, as they will see through those who are not pure of heart.

Not understanding the many rules of Logos, Hudson is quickly saddled with a troll curse. Charlotte, who, along with her father, was banished from Logos, can help get rid of the curse--but only if he agrees to find the lost Princess of Logos in return.