The Abandoned — Paul Gallico

A classic feline fairytale set in England about a boy who transforms into a cat following a tragic incident -- from the author of The Snow Goose and Mrs. ‘Arris Goes to Paris
 
London hasn't been kind to Peter, a lonely boy whose parents are always out at parties, and though Peter would love to have a cat for company, his nanny won't hear of it. One day, Peter sees a striped kitten in the park across from his house. Crossing the road on his way to the tabby, he is struck by a truck.

Everything is different when Peter comes to: He has fur, whiskers, and claws; he has become a cat himself! But London isn't any kinder to cats than it is to children. Jennie, a savvy stray who takes charge of Peter, knows that all too well. Jennie schools young Peter in the ways of cats, including how to sniff out a nice napping spot, the proper way to dine on mouse, and the single most important tactic a cat can learn: “When in doubt, wash.” Jennie and Peter will face many challenges -- and not all of them are from the dangerous outside world -- in their struggle to find a place that is truly home.