Nick always had to shake his head sadly and then Aunt Glenda would smile triumphantly. On the day when she decided never to take us to Harrods with her again, Nick had surprised me by changing his tactics. Tiny and plump-cheeked at the time—he was such a cute little boy, with an adorable lisp—he had stopped right in front of Aunt Glenda and asked, “Do you know what Mr. Grizzle said to me, Aunt Glenda? He said you’re a nasty frowsty old witch!” Of course Mr. Grizzle would never have said such a thing, he was much too polite, and Aunt Glenda was too good a customer, but my mum had said something rather like it the evening before. Aunt Glenda pressed her lips together and stalked on, holding Charlotte’s hand. Back home there had been an unpleasant scene with my mother, who was cross because we’d had to find our way home on our own, and Aunt Glenda had said in icy tones that Mum was responsible for the frowsty witch remark, and the upshot was that we weren’t allowed to go shopping with Aunt Glenda ever again. But even now we liked saying “frowsty.”

When I got older, I stopped telling people I could see things that they couldn’t. That’s best if you don’t want to be thought crazy. But I never had to pretend to Nick, Caroline, and Lesley, because they believed in my ghosts. I wasn’t quite sure about Mum and Great-aunt Maddy, but at least they never laughed at me. Aunt Maddy had strange visions herself at irregular intervals, so she probably knew just how it felt when no one believed you.

“Is he nice?” whispered Nick. The beam of his flashlight danced over the stairs.

“Who?”

“Your ghost, of course.”

“It all depends,” I said truthfully.

“What does he look like?”

“He’s rather cute. But he thinks he’s dangerous.” As we went down on tiptoe to the second floor, which was occupied by Aunt Glenda and Charlotte, I tried describing Xemerius as well as I could.

“Cool,” whispered Nick. “An invisible pet! I wish I had one!”

“Pet! Don’t you ever say that when Xemerius is within earshot!” I half hoped to hear my cousin snoring through her bedroom door, but of course Charlotte didn’t snore. People who are perfect don’t make nasty, frowsty noises in their sleep.

Halfway down to the next floor, my little brother yawned, and I instantly felt guilty. “Listen, Nick, it’s three thirty in the morning, and you have to go to school later. Mum will murder me if she finds out I’ve kept you awake.”

“I’m not a bit tired! And it would be mean of you to leave me out now! What did Grandfather hide in the chest?”

“I’ve no idea. Maybe a book explaining everything to me. Or at least a letter. Grandpa was Grand Master of the Lodge and its Guardians. He knew all about me and this time-travel stuff, and by the time he died, he knew it wasn’t Charlotte who inherited the gene. Because I met him in the past, in person, and explained it all to him.”

“You’re so lucky,” whispered Nick, adding almost as if ashamed of himself, “To be honest, I can hardly remember him. But he was always good-tempered and not a bit strict, just the opposite of Lady Arista. And he used to smell of caramel and something herby.”

“That was the tobacco he smoked in his pipe—careful!” I stopped Nick just in time. By now we were past the second floor, but there were a few tricky steps on the stairs down to the first floor that creaked badly. Years of sneaking down to the kitchen by night had taught me to avoid them. We carefully walked around the creaking places, and finally reached Great-great-great-great-great-uncle Hugh’s portrait.

“Okay. Here we are.”

Nick shone his flashlight on our ancestor’s face. “It was mean of him to call his horse Fat Annie! She’s lovely and slender—he’s the one who looks like a fat pig with whiskers.”

“I agree with you.” I was feeling behind the picture frame for the bolt that started the mechanism to open the secret door. As usual, it stuck a bit.

“All sleeping like babies.” Xemerius landed on the stairs beside us, puffing. “That’s to say, all but Mr. Bernard. He obviously suffers from insomnia, but don’t worry. He’s eating a plate of cold chicken in the kitchen and watching a Clint Eastwood film.”

“Good.” The picture swung out with its usual squealing sound, showing a few steps fitted between the walls. They ended only about six or seven feet away in front of another door. This door led into the first-floor bathroom, and it was hidden on the bathroom side by a floor-length mirror. We often used to come through it for fun—we got our kicks by not knowing if there’d be anyone in there using the bathroom—but we hadn’t yet found out what the point of this secret passage was. Maybe one of our ancestors had just thought it would be nice to be able to get away to this quiet place whenever he liked.

“So where’s the chest, Xemerius?” I asked.

“On the left. Between the wallsh.” I couldn’t make him out clearly in the dim light, but it sounded as if he was picking something out of his teeth.

“Xemerius is a bit of a tongue-twister,” said Nick. “I’d call him Xemi. Or Merry. Can I go in and get the chest?”

“It’s on the left,” I said.

“Tongue-twishter yourshelf,” said Xemerius. “Shemi or Merry—no way! I come from a long line of mighty ansheshtral demonsh, and our namesh—”

“Have you got something in your mouth?”

Xemerius spat and smacked his lips. “Not now. I ate the pigeon I found asleep on the roof. Stupid feathers.”

“But you can’t eat at all!”

“No idea of anything, but always giving us the benefit of her opinion!” said Xemerius, offended. “Won’t even let me eat a little pigeon!”

“You can’t eat a pigeon,” I repeated. “You’re a ghost.”

“I’m a demon! I can eat anything I like! I once ate a whole priest. Vestments and all. Why are you looking at me so incredulously?”

“Why don’t you keep your eyes open for anyone coming?”

“Hey, don’t you believe me?”

Nick had already climbed down the steps into the bathroom and was shining his flashlight along the wall. “I can’t see anything.”

“The chest is behind the brickwork, like I said. In a hollow space, bonehead,” said Xemerius. “And I’m not lying. If I say I ate a pigeon, then I did eat a pigeon.”

“It’s in a hollow space behind the brickwork,” I told Nick.

“But I can’t see a loose brick anywhere.” My little brother knelt down on the floor and pressed his hands against the wall, testing it out.

“Hello-o-o, I’m speaking to you!” said Xemerius. “Are you ignoring me, crybaby?” When I didn’t reply, he said, “Well, okay, so it was the ghost of a pigeon. Comes to the same thing.”

“Ghost of a pigeon—are you trying to be funny? Even if pigeons did have ghosts—and I’ve never seen one—you still couldn’t eat them. Ghosts can’t kill one another.”

“These bricks are all solid as rocks,” said Nick.

Xemerius snorted angrily. “First, even pigeons can sometimes decide to stay on the earth and haunt it, don’t ask me why. Maybe they have unfinished business with a cat somewhere. Second, kindly tell me how you can tell a ghost pigeon from all the other pigeons. And third, their ghostly life is over if I eat them. Because as I’ve told you I don’t know how often, I’m no ordinary ghost. I’m a demon! Maybe I can’t do much in your world, but I’m big news in the world of ghosts. When will you finally get the hang of that?”

Nick stood up again and kicked the wall a couple of times. “Nope, nothing we can do about it.”

“Ssh! Stop that, it makes too much noise.” I put my head into the bathroom and looked at Xemerius reproachfully. “So you’re big news. Great. Now what?”

“How do you mean? I never said a word about loose bricks.”

“Then how are we to get at the chest?”

“With a hammer and chisel.” That was a very helpful answer, only it wasn’t Xemerius who gave it, but Mr. Bernard. I froze with horror. There he stood, only a couple of feet above me on the steps. I could see his gold-rimmed glasses sparkling in the dark. And his teeth. Could he be smiling?

“Oh, shit!” Xemerius was so upset that he spat out water on the carpet over the steps. “He must have inhaled the cold chicken to get it inside him so fast. Or else the film was no good. You can’t rely on Clint Eastwood these days.”

Unfortunately I was unable to say anything but “Wh-what?”

“A hammer and chisel would be the best solution,” repeated Mr. Bernard calmly. “But I suggest you put it off until later. If only so as not to disturb the rest of the family when you take the chest out of its hiding place. Ah, I see Master Nick is here too.” He looked into the beam of Nick’s flashlight without blinking. “Barefoot! You’ll both catch your death of cold.” He himself was wearing slippers and an elegant dressing gown with an embroidered monogram, WB. (Walter? William? Wilfred?) I’d always thought of Mr. Bernard as a man without any first name.

“How do you know it’s a chest we’re looking for?” asked Nick. His voice didn’t tremble, but I could tell from his wide eyes that he was as startled and baffled as I was.

Mr. Bernard straightened his glasses. “I expect because I walled up that—er—that chest in there myself. It’s a kind of wooden box decorated with valuable inlaid intarsia work, an antique from the early eighteenth century that belonged to your grandfather.”

“And what’s in it?” I asked, finding that I could speak again at last.

Mr. Bernard looked at me with reproof in his eyes. “Naturally it was not for me to ask that question. I simply hid the chest here on behalf of your grandfather.”

“He can’t try telling me that,” said Xemerius grumpily. “Not when he goes around poking his nose into everything else. And slinking along here after lulling a person into a false sense of security with cold chicken. But it’s all your fault, you silly watering can! If you had believed me, the senile old sleepwalker could never have taken us by surprise!”

“I will of course be happy to help you to extricate the chest again,” Mr. Bernard went on. “But preferably this evening, when your grandmother and aunt will be on their way to the meeting of the ladies of the Rotary Club. So I suggest that we all go back to bed now. After all, you two have to go to school later.”

“Yes, and meanwhile he’ll hack the thing out of the wall himself,” said Xemerius. “Then he can get his hands on the diamonds and leave a few withered old walnuts for us to find. I know his sort.”

“Don’t be daft,” I muttered. If Mr. Bernard had wanted to do anything like that, he could have done it long ago, because no one else knew a thing about that chest. What on earth could be in it for Grandpa to have wanted it bricked up inside his own house?