“It’s not as if you were going to meet old school friends who might laugh at you there,” said Mr. de Villiers.

“No,” said Gideon, putting my hat down on a table. “More likely I’ll meet guys wearing embroidered pink breeches who think they look terrific,” he said, shaking his head. At first I’d had to let my eyes adjust to the light. Now I looked curiously around. The room had no windows, as I’d expected, and there was no fireplace either. I couldn’t see a time machine anywhere. Only a table and a few chairs, a chest, a cupboard, and some kind of saying in Latin carved into the stone wall.

Mr. de Villiers gave me a friendly smile. “Blue suits you wonderfully, Gwyneth. And Madame Rossini has done something very elegant to your hair.”

“Er … thank you.”

“We’d better hurry up. I’m dying of heat in these clothes.” Gideon undid his coat so that I could see the sword hanging from his belt.

“Come over here.” Dr. White went up to the table and revealed something that had been wrapped in red velvet. At first glance it looked like a large clock, the kind you might stand on a mantelpiece. “I’ve adjusted all the settings. The window of time available to you two is three hours.”

At a second glance, I realized it wasn’t a clock. It was a strange device made of polished wood and metal with any amount of knobs, flaps, and little wheels. All the surfaces were painted with miniature pictures of the sun, moon, and stars, and inscribed with mysterious signs and patterns. It was curved like a violin case and set with sparkling jewels, great big ones that couldn’t possibly be real.

“Is that the chronograph? It’s so small!”

“It weighs nine pounds,” said Dr. White, sounding as proud as a father telling you the weight of his newborn baby. “And before you ask, yes, the stones are all genuine. This ruby alone is six carats.”

“Gideon will go first,” said Mr. de Villiers. “The password?”

“Qua redit nescitis,” said Gideon.

“Gwyneth?”

“Yes?”

“The password!”

“What do you mean, password?”

“Qua redit nescitis,” said Mr. de Villiers. “The password of the Guardians for this twenty-fourth of September.”

“But it’s the sixth of April.”

Gideon turned his eyes to heaven. “We arrive on the twenty-fourth of September inside this house. If we don’t want the Guardians to chop off our heads, we have to know the password. Qua redit nescitis. Go on, repeat it.”

“Qua redit nescitis,” I said. I was never going to be able to remember that for longer than a second. There, now it was gone again. Maybe I could write it on a scrap of paper. “What does it mean?”

“Don’t tell me you’re not learning Latin at school!”

“Well, I’m not,” I said. I was taking French and German at school, which was more than enough.

“In full, Qua redit nescitis horam. “You know not the hour of your return,” said Dr. White.

“Rather a flowery translation!” said Mr. George. “One could also say, ‘You don’t know when—’”

“Gentlemen!” Mr. de Villiers tapped his wristwatch in a meaningful way. “We don’t have forever. Ready, Gideon?”

Gideon held his hand out to Dr. White, who raised one of the flaps and put Gideon’s forefinger in the opening behind it. There was a faint humming sound as if cogwheels had started moving inside the device. It was almost like a tune on a music box. One of the jewels, a huge diamond, suddenly lit up from inside and bathed Gideon’s face in clear white light. At the same moment, he disappeared.

“Wow, out of this world,” I whispered, impressed.

“Literally so,” said Mr. George. “Your turn now. Stand exactly here.”

Dr. White went on. “And remember what we’ve told you: do as Gideon says and, whatever happens, always keep close to him.” He took my hand and placed my forefinger in the opening under the flap. Something sharp pricked my fingertip, and I flinched. “Ow!”

Dr. White held my hand firmly down inside the flap. “Don’t move!”

This time a big red stone on the chronograph began shining. Red light dazzled me. The last thing I saw was my huge hat lying forgotten on the table. Then everything around me went dark.