Molly reached out for it, and I handed it over. She muttered some Words over the mirror, made a few quick gestures, and even held it upside down and shook it in the hope something might fall out, but nothing happened. Molly sniffed and handed the mirror back to me.

“All right,” she said. “I’ll bite. What’s it supposed to do?”

“It can be used to make contact with other members of the Drood family, in the past or the future, to ask them for advice or information.”

There was a pause, and then Molly said, “No offence guys, but I think you got stiffed on the deal. I mean, it’s not the most useless magic object I’ve ever seen . . . but it comes pretty damned close.”

“You’re a witch,” the Armourer said kindly, “and therefore used to thinking mainly in terms of the here and now. The Glass has many uses. Vital information lost in this time can be found in the past, before it was lost. Or in the future, after it has been rediscovered. The greatest family tacticians, of the past or the future, are now ours to consult. We can even take specific advice from the future, on which matters to pursue and which are best left strictly alone . . .”

“If this Glass is so useful,” I said, “how did it happen to go missing for so long?”

“Ah,” said the Armourer reluctantly. “There are many stories about that. The one I tend to believe the most, because I dislike it the most, is that someone asked the Glass a very specific question, and got a very specific answer that disturbed the shit out of him. So he took the Glass and hid it, to prevent anyone else from asking the question, or learning the answer.”

“I can’t see this family giving up anything that useful so easily,” said Molly.

“I can,” I said. “The Droods have always been very cautious about anything involving time travel. Ever since the Great Time Disaster of 1217, when the family almost wiped itself out after inadvertently setting up a Möbius-strip time paradox. There’s still some rooms in the Hall we can’t find, because of what we had to do to break free. And we don’t even think about what might still be happening to the poor bastards we had to abandon in those rooms. The human mind just isn’t equipped to deal with all the possible complications and downright nasty ramifications of mucking about with time.”

And then I stopped short as an idea came to me, hitting me hard enough to stop my breath, while a cold hand curled around my heart. I looked into Merlin’s Glass, and my face stared back at me, so cold and harsh and determined I barely recognised it.