The Book Cat by Polly Faber

Morgan is a young orphan who lives off scavenging - until he finds a cozy home at a famous London publishing house. Over time he learns a trade - and soon becomes the very best book cat in the business. And then the Blitz begins. Morgan finds himself training up twenty-odd kittens to be bookcats, and then there is the small matter of secretly evacuating them out of London. Happily, Morgan has a plan.