“You’ve been crying,” my mother had said in a matter-of-fact way.

“There, you see?” Xemerius had said. “Now she’s going to squeeze you like a lemon until the pips squeak. She won’t let you out of her sight for a second, and we can wave good-bye to tonight’s treasure hunt.”

I’d made a face at him, to let him know that I didn’t feel like treasure hunting tonight anymore. Well, you have to make faces at invisible friends if you don’t want other people to think you’re crazy because you talk to the empty air.

“Tell her you were trying out the pepper spray,” the empty air had answered me back, “and it got into your own eyes by mistake.”

But I’d been far too tired to tell lies. I just looked at my mum with red-rimmed eyes and tried telling the truth. Here goes, then, I’d thought. “It’s just … no, I don’t feel too good. It’s … kind of a girl thing, you know?”

“Oh, darling.”

“If I phone Lesley, I know I’ll feel better.”

Much to the surprise of Xemerius—me too—Mum had been satisfied with this explanation. She made me peppermint tea, left the teapot and my favorite cup with its pattern of spots on my bedside table, stroked my hair, and otherwise left me in peace. She didn’t even keep reminding me of the time, as usual. (“Gwyneth! It’s after ten, and you’ve been on the phone for forty minutes. You’ll be seeing each other at school tomorrow.”) Sometimes she really was the best mother in the world.

Sighing, I swung my legs over the edge of the bed and stumbled off to the bathroom. I felt a cold breath of air.

“Xemerius? Are you there?” I asked under my breath, and felt for the light switch.

“That depends.” Xemerius was dangling head down from the ceiling fixture in the corridor, blinking at the light. “I’m here so long as you don’t turn back into a watering can.” He raised his voice to a shrill, tearful pitch as he imitated me—rather well, I’m sorry to say. “And then he said, I have no idea what you’re talking about, and then I said, yes or no, and then he said, yes, but do stop crying.…” He sighed theatrically. “Girls get on my nerves worse than any other kind of human being. Along with retired taxmen, saleswomen in hosiery departments, and presidents of community garden societies.”

“I can’t guarantee anything,” I whispered, so as not to wake the rest of my family up. “We’d better not mention You Know Who, or the indoor fountain will come back on again.”

“I was sick of the sound of his name anyway. Can we do something sensible for a change? Go treasure hunting, for instance?”

Getting some sleep might have been sensible, but unfortunately I was wide awake now. “Okay, we can start if you like. But first I have to get rid of all that tea.”

“What?”

I pointed to the bathroom door.

“Oh, I see,” said Xemerius. “I’ll just wait here.”

I looked better than I expected in the bathroom mirror. Unfortunately there wasn’t a sign of galloping consumption. My eyelids were a little swollen—that was all, as if I’d been using pink eye shadow and put on too much.

“Where were you all this time, Xemerius?” I asked when I came out into the corridor again. “Not by any chance with…?”

“With whom?” Xemerius looked indignant. “Are you asking me about the person whose name we don’t mention?”

“Well, yes.” I would have loved to know what Gideon did yesterday evening. How was the wound in his arm healing up? And had he maybe said something to anyone about me? Like It’s all a terrible misunderstanding. Of course I love Gwyneth. I wasn’t pretending at all when I told her so.

“Oh, no you don’t! I’m not falling for that one.” Xemerius spread his wings and flew down to the floor. When he was sitting there in front of me, he hardly came above my knee. “But I didn’t go out. I was having a good look around this house. If anyone can find that treasure, then I can. If only because none of the rest of you can walk through walls. Or rummage around in your grandmother’s chest of drawers without being caught at it.”

“Yes, there must be some advantages to being invisible,” I said. I didn’t point out that Xemerius couldn’t rummage around in anything because his ghostly claws couldn’t even open a drawer. No ghost I’d ever met could move objects. Most of them, unlike Xemerius, couldn’t even manage a breath of cold air. “But you know we’re not looking for a treasure, only something left by my grandfather that will help us to find out more.”

“This house is full of stuff that might be treasure. Not to mention all the possible hiding places for it,” Xemerius went on, taking no notice of me. “Some of the walls on the first floor are double, with passages in between them—passages so narrow you can tell they’re not built for people with big bums.”

“Really?” I’d never discovered those passages myself. “How do you get into them?”

“The doors are covered up with wallpaper in most of the rooms, but there’s still a way in through your great-aunt’s wardrobe and another behind that big, solid sideboard in the dining room. And one in the library, hidden behind a swiveling bookcase. Oh, and there’s a link between the library and the stairwell leading to Mr. Bernard’s rooms, and another going up to the second floor.”

“Which would explain why Mr. Bernard always seems to appear out of nowhere,” I murmured.

“And that’s not all. There’s a ladder inside the big chimney shaft on the wall next to number 83 next door. You can climb it all the way up to the roof. You can’t get into the shaft from the kitchen anymore, because the old fireplace there has been bricked up, but there’s a way in with a flap over it at the back of the built-in cupboard at the end of the first-floor corridor, big enough to let Santa Claus through—or your weirdo of a butler.”

“Or the chimney sweep.”

“And then there’s the cellar!” Xemerius acted as if he hadn’t heard my down-to-earth remark. “Do your neighbors know this house has a secret, and there’s a second cellar underneath the cellar that everyone knows about? Although if you go looking for anything there, you’d better not be scared of spiders.”

“Then we’d better look somewhere else first,” I said, quite forgetting to whisper.

“If we knew what we’re looking for, of course it would be easier.” Xemerius scratched his chin with one of his back paws. “I mean, basically it could be anything: the stuffed crocodile in the recess, the bottle of Scotch behind the books in the library, the bundle of letters in the secret drawer of your great-aunt’s desk, the little chest in a hollow place in the brickwork—”

“A chest in the brickwork?” I interrupted him. And what recess was he talking about?

Xemerius nodded. “Oh, dear, I think you’ve woken your brother up.”

I spun round. My twelve-year-old brother, Nick, was standing in the doorway of his room, running both hands through his untidy red hair. “Who are you talking to, Gwenny?”

“It’s the middle of the night,” I whispered. “Go back to bed, Nick.”

Nick looked at me undecidedly, and I could see him waking up more and more every second. “What was all that about a chest in the brickwork?”

“I … I was going to look for it, but I think I’d better wait until it’s light.”

“Nonsense,” said Xemerius. “I can see in the dark like a … well, let’s say an owl. And you can’t very well search the house when everyone’s awake. Not unless you want even more company.”

“I can bring my flashlight,” said Nick. “What’s in the chest?”

“I don’t know exactly.” I thought for a moment. “It could be something left there by Grandpa.”

“Oh,” said Nick, interested. “And whereabouts is this chest hidden?”

I looked inquiringly at Xemerius.

“I saw it to one side of the secret passage behind that fat man with whiskers, the one sitting on his horse,” said Xemerius. “But who goes hiding secrets—I mean treasures—in a boring old chest? I think the crocodile is much more promising. Who knows what it’s stuffed with? I’m in favor of slitting it open.”

I wasn’t. I had an idea I’d met that crocodile before. “Let’s look in the chest first. A hollow place doesn’t sound bad.”

“Boring, boring, boring!” repeated Xemerius. “One of your ancestors probably hid his tobacco from his wife in it … or…” Obviously he had just had an idea he liked, because now he suddenly grinned. “Or the chopped-up body of a maid who stepped off the straight and narrow and went astray!”

“The chest is in the secret passage behind the picture of Great-great-great-great-great-uncle Hugh,” I explained to Nick. “But—”

“I’ll just get that flashlight!” My brother had already turned back to his room.

I sighed.

“Why are you sighing again?” Xemerius rolled his eyes. “It can’t hurt if your brother comes along.” He spread his wings. “I’ll just do a round of the house and make sure the rest of the family are fast asleep. We don’t want that sharp-nosed aunt of yours catching us when we find the diamonds.”

“What diamonds?”

“Think positive for once!” Xemerius was already hovering in the air. “Which would you rather, diamonds or the remains of a murdered maidservant? It’s all a question of attitude. We’ll meet in front of your fat uncle on his horse.”

“Are you talking to a ghost?” Nick had reappeared behind me. He switched off the ceiling light in the corridor and put his flashlight on instead.

I nodded. Nick had never doubted that I really could see ghosts—quite the opposite. Even when he was only four and I was eight, he used to stand up for me if people didn’t believe it. Aunt Glenda, for instance. We always quarreled when she went to Harrods with us and I talked to the nice uniformed doorman Mr. Grizzle. Mr. Grizzle had been dead for fifty years, so of course people wondered why I stopped and started talking about the Royal Family (Mr. Grizzle was a great admirer of the Queen) and the unseasonably wet June we were having (the weather was Mr. Grizzle’s second favorite subject of conversation). A lot of passersby laughed, some said children had such wonderful imaginations (ruffling up my hair to emphasize their point), and many others shook their heads, but no one got as worked up as Aunt Glenda. She used to look terribly embarrassed and haul me on after her, scolding if I braced my feet and stood my ground. She said I ought to follow Charlotte’s example (even then, Charlotte was so perfect that she never lost a barrette out of her hair), and worst of all, she threatened me with getting no dessert that evening. But although she carried out her threat (and I loved all desserts, even stewed plums), I simply couldn’t bring myself to walk past Mr. Grizzle without a word. Nick always tried to help by begging Aunt Glenda to let go of me because there was no one else for poor Mr. Grizzle to talk to, and Aunt Glenda cleverly got the better of him by saying, in sugary sweet tones, “Oh, little Nick, when will you understand that your sister is just trying to attract attention? There are no such things as ghosts. Do you see a ghost here?”