Leonard has never had a name. Or a body. Or a best friend. But he is excited to try being a human. On their three-hundredth-birthday, every alien from Leonard's home galaxy gets to spend a month in the body of an Earth Creature. Leonard was supposed to become a forest ranger in Yellowstone National Park - but there was a mix-up. And now he's stuck as a stray cat. Luckily for Leonard, he meets a young human called Olive - and together they set out on a journey to find home.