Tilly Millpepper and the Wishing Stone

What would you wish for if you were given a wishing stone? Yes, a real wishing stone because that's what Uncle Leonardo gave Tilly Millpepper on her tenth birthday. As things turned out, it was just the beginning of her magical adventures.
When she and her family move temporarily from London to a large house in the Essex countryside, they discover several unexpected animals, including a pony for Tilly to learn to ride. But that's not all they discover, for there is also a creepy witch-like housekeeper, who seems to be looking for something.