Shoji began hitting keys on the keyboard. “ ‘This is not a chemistry class we are talking about, Mr. Fujisaki,’ ” he said in the prissy voice as he typed. “ ‘This is the space-time continuum.’ ”

The curtains began, awkwardly, to rise.

“I know it’s the continuum,” Jim said, “but—”

“Jim,” Lizzie said, still out of sight but not for long, and both of them turned to look at her. “Will you ask him at least?” she said. “It means—”

And I found myself in a corner of Blackwell’s Book Store. Its dark woods and book-lined walls are not only instantly recognizable but timeless, and for a moment I thought I’d made it back to 2057, and getting to the lab was going to be a simple matter of sprinting up the Broad to Balliol, but as soon as I poked my head round the bookcase, I knew it wasn’t going to be that simple. Outside Blackwell’s bow windows it was snowing. And there was a Daimler parked in front of the Sheldonian.

Not Twenty-First Century, and now that I looked around, not the end of Twentieth either. No terminals, no paperbacks, no print-and-binds. Hardbacks, mostly without dust jackets, in blues and greens and browns.

And a shop assistant bearing down on me with a notebook in her hand and a yellow pencil behind her ear.

It was too late to duck back into a corner. She’d already seen me. Luckily, men’s clothes, unlike women’s, haven’t changed that much over the years, and boating blazers and flannels can still be seen in Oxford, though usually not in the dead of winter. With luck, I could pass as a first-year student.

The shop assistant was wearing a slimmish navy-blue dress Verity would probably have been able to date to the exact month, but the mid-Twentieth Century decades all look alike to me. 1950? No, her pencil-decked hair was put up in a severe knob, and her shoes laced. Early 1940s?

No, the windows were intact, there weren’t any blackout curtains and no sandbags piled up by the door, and the clerk looked far too prosperous to be post-war. The Thirties.

Verity’s regular assignment was the Thirties. Maybe the net had mistakenly sent me to the coordinates of one of her old drops. Or maybe she was here.

No, she couldn’t be here. My clothes might pass, but not her long, high-necked dress and piled-up hair.

The range of times and places she could be without creating an incongruity just by her appearance was very limited, and most of them were civilized, thank goodness.

“May I help you, sir?” the shop assistant said, looking at my mustache disapprovingly. I’d forgotten about it. Had men been clean-shaven in the 1930s? Hercule Poirot had had a mustache, hadn’t he?

“May I help you, sir?” she repeated, more severely. “Is there a particular book you are looking for?”

“Yes,” I said. And what books would they have had in Blackwell’s in Nineteen-Thirty-What? The Lord of the Rings? No, that was later. Goodbye Mr. Chips? That had been published in 1934, but what was this? I couldn’t see a date on that salespad of the shop assistant’s, and the last thing we needed, with the continuum falling down around our ears, was another incongruity.

“The Decline and Fall of the Roman Empire,” I said to be safe. “By Gibbon.”

“That would be on the first floor,” she said. “In History.”

I didn’t want to go up to the first floor. I wanted to stay close to the drop. What was on this floor? Eighty years from now, it would be metafiction and self-writes, but I doubted they had either here. Through the Looking Glass? No, what if children’s lit was already in a separate shop?

“The stairs up to the first floor are just there, sir,” she said, removing her pencil from behind her ear and pointing with it.

“Have you Jerome’s Three Men in a Boat?” I said.

“I will have to check,” she said, and started toward the rear.

“To Say Nothing of the Dog,” I called after her, and, as soon as she had rounded a bookcase, darted back to my corner.

I had been half-hoping the net would be open, or faintly shimmering in preparation, but there was nothing in the ceiling-to-floor rows of books to indicate it had ever been there. Or to give me a clue to what year I was in.

I began taking down books and opening them to the title page. 1904. 1930. 1921. 1756. That’s the trouble with books. They’re timeless. 1892. 1914. No date. I flipped the page over. Still no date. I flipped the page back again and read the title. No wonder. Herodotus’s History, which the Colonel and Professor Peddick had been reading only yesterday.

The bell over the door jangled. I peered carefully round the corner, hoping it was Verity. It was three middle-aged women in fur stoles and angle-brimmed hats.

They stopped just inside the door, brushing snow lovingly off their furs as if they were pets, and talking in high nasal tones.

“…and eloped with him!” the one on the right said. Her fur looked like a flattened version of Princess Arjumand. “So romantic!”

“But a farmer!” the middle one said. Her fur looked more like Cyril and was nearly as wide.

“I don’t care if he is a farmer,” the third one said. “I’m glad she married him.” She had the best fur of all, an entire string of foxes with their heads still on and bright little glass eyes. “If she hadn’t, she’d still be trapped in Oxford, serving on church committees and running jumble sales. Now, what was it I wanted to buy? I said to Harold this morning, I must remember to buy that when I go to Blackwell’s. Now, what could it have been?”

“I must get something for my godchild for her birthday,” the one with Cyril on her shoulders said. “What should I get? Alice, I suppose, though I’ve never understood why children like it. Going from place to place with no rhyme or reason. Appearing and disappearing.”

“Oh, look!” the string of foxes said. She had picked up a book with a green dust jacket from a display table. Her fox-colored gloved hand was over the title, but I could see the author’s name: Agatha Christie.

“Have you read her latest?” she said to the others.

“No,” the one with Cyril on her shoulders said.

“Yes,” the Princess Arjumand said, “and it—”

“Stop,” the string of foxes said, raising her gloved hand in warning. “Don’t tell me the ending.” She turned back to Cyril. “Cora always ruins the ending. Do you remember The Murder of Roger Ackroyd?”

“That was different. You wanted to know what all the fuss in the papers was about, Miriam,” the Princess Arjumand said defensively. “I couldn’t explain it without telling who the murderer was. At any rate, this one isn’t anything like Roger Ackroyd. There’s this girl who someone is attempting to murder, or at least that’s what one’s supposed to think. Actually—”

“Don’t tell me the ending,” the Little Foxes said.

“I didn’t intend to,” the Princess Arjumand said with dignity. “I was simply going to say that what you think is the crime, isn’t, and things aren’t at all what they seem.”

“Like in The Fountain Pen Mystery,” the Cyril-draped one said. “What you think is the first crime turns out to be the second. The first one had happened years before. Nobody even knew the first crime had been committed, and the murderer—”

“Don’t tell me,” the Little Foxes said, clapping fox-gloved hands to her ears.

“The butler did it,” the Cyril said.

“I thought you hadn’t read it,” the Little Foxes said, taking her hands down from her ears.

“I didn’t,” she said. “It’s always the butler,” and the lights went out. But it was daytime, and even if something had happened to the electricity, there would still be enough light from Blackwell’s bow windows to see by.

I put my hand out to the bookshelf in front of me and felt it cautiously. It felt clammy and hard, like stone. I took a cautious step toward it. And nearly pitched forward into emptiness.