It's a tale you don't hear about too often, but it is a good one.
Written by J.R.R. Tolkien, it's the story of a little dog named Rover and the adventures he has after being turned into a toy by a wizard.
An easy read, if you like other books by Tolkien and fairy tales, I recommend you give it a go. The places and creatures he describes are very imaginative and it contains some lovely ideas. For example: a seagull that flies to the moon with messages for the wizard who lives there with a little white flying dog.
I don't want to say too much because it's lovelier if you read it for yourself.
The edition at my house even has illustrations by Tolkien himself!
I find his depictions of mermaids interesting because one of them married a wizard and they moved to the land. He mentions mermaid tails with aversion. He remarks on her "deplorable" tail. Having a fish tail would certainly be shocking for humans to see, but he seems to disdain them for some reason in the midst of all the unusual things that are going on. Is he just projecting the views of the two-legged people's society (from the story) into his narration, or is it something else?