User blog:Cloudmonkey/Book Talk: Dogsbody by Diana Wynne Jones

Sirius, the Dog Star, is a luminary, one of the high effulgents, used to standing in judgment over the lesser luminaries. Now, however, he himself stands falsely accused of murdering a fellow luminary and grossly misusing a Zoi to commit that murder, leading to the loss of the Zoi. Polaris hands down the sentence: Sirius is to be stripped of his position and banished to the body of a creature native to the sphere where the missing Zoi is thought to have fallen. If, during the lifespan of that creature, he is able to retrieve the Zoi, the court will reinstate his position. Otherwise, he will simply die when the body of the creature dies.

Sirius wakes in the body of a puppy. Weak and hungry, he has thought for nothing but fighting for food among a warm bundle of creatures like himself. Not yet weaned, he and his fellow puppies are put in a sack and thrown in the river to drown. Somehow Sirius fights his way free of the sack and reaches the river's edge. There he is found and adopted by Kathleen, a young Northern Irish girl who is as powerless as Sirius once was powerful, who is only able to persuade her aunt Duffie to let her keep Sirius by promising to do all the housework and cooking.

Somehow Sirius must recover his memories, learn about the world he's found himself in, find the Zoi, and prove his innocence, all while avoiding Duffie's threats to have him taken to the vet to be put to sleep.