Crenshaw by Katherine Applegate is bigger than what a single introductory sentence can describe. Jackson and his family are facing homelessness again. He can remember the last time they were but his sister doesn't.
Children in need — no, people in need — resort to their imagination. Imagination to find a happier place, imagination to think of a way out, imagination for fantasy. Sometimes it's an imaginary friend to talk to, to see guidance from. Now, what if that imaginary friend was real.
Crenshaw is Jackson's imaginary friend. He's a six foot tall, talking cat. He's not there to actually rescue Jackson from his problems. He's there to help him cope.
Crenshaw is what I'd call a pooka. He's a feline manifestation just as Harvey is a lagomorph manifestation. He's also a kinder and more gentle pooka, rather than being a creature who enjoys tormenting alcoholics.