I liked the last Diana Wynne Jones books I read so much that I was eager to pick this one up, especially since it had won some award or other (checking...) OK, it was an ALA Notable Book and "Commended" by the Carnegie Medal. Fine. However, unlike many of Wynne Jones' stories, I felt that this was definitely a ‘kids' book.. I would recommend that any small child who has a dog read it for the insights into how a pet dog thinks. But I didn't really get into it that much.
The story is that Sirius, the Dog Star, is condemned by a court of his fellow luminaries for an alleged crime, and is sentenced to live out his life in the body of a dog, here on earth. He's born into the form of a puppy which gets adopted by a young Irish girl, Kathleen, and becomes torn between helping her in her bad home situation and remembering/trying to accomplish the quest that has been assigned to him on earth, to find a lost object of power and redeem himself in the view of his peers.
As I said, it's very effective in recreating the thought processes of a dog, but the story wasn't really complex or sophisticated enough to find satisfying, for me.