Interesting book with a lot of great world building.

Emma's human family has to move into a trailer alongside crags, a term used for any magical creature, because they have used much of their finances up in order to look for Emma's missing sister, Helena. Emma discovers Jack, a cat, living in their trailer.

Jack isn't just any cat. He used to be a magical cat like all other cats. He is trying to keep away from the rest of his pride, who are trying to kill him. He figures out a way for Emma to get magic so that she can use that magic to find her sister, and it changes her in more ways than she expected.