What are the motifs in Wondrous Strange by Lesley Livingston?

Good vs evil is a reoccurring idea in the story. The gate that separates the Otherworld from the mortal world is a dividing line between that of good and evil. Once the gates were closed and locked, the forbidden mortal world turned many of the Fair Folk into evil beasts and monsters in an effort to breach the gate and make their way into the mortal world.