The Ghost of Opalina, or Nine Lives, by Peggy Bacon (1967), is an utterly charming cat ghost fantasy story.
It starts in my most favorite way: "Phillip, Ellen, and Jeb Finley lived in the city until young Jeb was five years old. Then their parents bought a house near the village of Heatherfield, and, in late August, they all went to live in the country.
The house was large, rambling, and very old, set down on thick soft lawns like green fur, with wads of moss under the big old trees. There were old barns, old gardens full of box, a lily pool, old-fashioned flowers and shrubs."
I love books about children moving to old houses with lovely gardens, so I was predisposed in the book's favor from the get go.
And then I met Opalina--an cat whose opinion of herself is worthy of an E. Nespit magical creature. She is the ghost of a cat who met an untimely end in the 18th century, and she manifests to the children, who are delighted to make her acquaintance. She regales them with tales of her various lives spent living in the old house, keeping a keen eye on its inhabitants, and haunting when necessary.
The book is episodic, in that each of Opalina's stories is its own self-contained unit of historical fiction, but that being said, the story of the house through time as told to its new inhabitants (who have their own difficulties to face fitting in to their new schools) makes a satisfying whole. Something of the same sort as happens, for instance, in The Sherwood Ring, by Elizabeth Marie Pope.
In addition, I was charmed (unexpectedly, cause often I don't notice these things) by the illustrations (which are the author's own). This one, in particular, tickles me tremendously:
That's Opalina, haunting the dog that killed her in comet-like form.
I highly recommend it to any reader of children's books who is both a cat lover and old house lover! I'm awfully glad it was still in my state's library system (too expensively out of print to buy--$800 on Amazon!), and thank you, those commentors who recommend it to me when I reviewed Caterpillar Hall!