Free Witch's Business by Diana Wynne Jones

Vernon.”
    â€œI wish it was,” Vernon said. Jess could see he was quite wretched about it.
    â€œLook, it’s our fault, too,” she said. “And we’ll find that necklace and spite her.”
    The problem, they soon realized, was where to start looking. The big house, across a large lawn, sitting up on a hill, was very big indeed. It was the kind of house which is all long, blank windows. Behind it, there were stables, sheds, greenhouses, and gardens. There seemed no end of possible places in which to hide necklaces.
    â€œIs it old at all?” Frank asked Martin, who came sauntering down the lawn to meet them. “I mean, could there be secret panels and things?”
    â€œNot that old,” said Martin. “There is paneling, but the builders had most of it out when we moved in. I know, because I was watching for hiding places. It was rather exciting, actually—except there wasn’t anything. But Vernon’s thought about it.”
    Vernon, who was still very miserable, sighed. “Like this,” he said. “If it was Biddy hid the stuff, she’d have to do it quick, not to be noticed. And there’s not many places left after the builders went at it. So I think we look in the ways out and in the sheds and gardens first.”
    â€œWhat if she buried it?” Jess asked.
    â€œIf she did that,” Vernon said, sounding very fierce, “then we’ll have to go and see her again. Maybe we can push her into dropping hints, like this morning.”
    â€œAnd push ourselves into Buster’s arms,” Frank said.
    â€œRisk that,” said Vernon. “It’s worth it. Let’s hunt.”
    They walked up the lawn, trying to decide who should look where. Frank became rather embarrassed. There seemed to be a lot of people around, peacefully walking about the lawn, or wandering in and out of the various doors of the house. They all stared curiously at the children. Some, who were playing croquet at one corner of the house, leaned on their mallets to watch them.
    â€œWho are they all?” Frank asked Martin.
    â€œThey’re the guests,” said Martin. “You knew this was a convalescent home, didn’t you?”
    Neither Frank nor Jess had known. They mumbled and tried to pretend they had.
    â€œWe have to call them guests,” Martin explained, “to humor them. They’re nearly all retired loonies really, you see, and we call them guests to show them how much better they are. But you don’t have to worry. They’re quite harmless and sensible most of the time.”
    After this explanation, Jess hurriedly suggested that she and Frank should hunt in the gardens. The idea of prying about in mad guests’ bedrooms was too much for her.
    â€œOkay,” said Martin. “Vernon can take on the back hall and the piece of paneling in the kitchens. I’ll do the rest indoors, and join you outside if we don’t find anything. Don’t take any notice of the guests. They’re all bored stiff and gape like fishes if anyone hiccups, but they’re quite harmless.”
    Harmless, Jess decided, was not quite the right word. This was after she had left Frank rooting about in the stables and set off by herself into the gardens at the back of the house. There were a whole lot more guests there. Two fat, red ones were playing tennis. A whole line more sat in deck chairs, with rugs over their knees, all along the back of the house. They were all elderly and, as soon as Jess appeared, all their heads turned, as if someone had threaded them on a string and then pulled it.
    Unfortunately, there was a long row of stone urns just in front of these guests. Jess went along, searching in each one, and the row of heads followed her every movement. Jess had found ten empty cigarette packets and an old lollipop, when one old lady could plainly bear no longer not knowing what Jess was looking for.
    â€œHave you lost anything,