Instead of leading us up as I expected, Jack guided us past the iron gate and further down the corridor to another set of descending stairs. I was becoming mightily frustrated with my footwear, the balls of my feet in great discomfort. But I didn't have time to think about it, as it turned out.

We had just reached the bottom of the stone steps when someone in the corridor above opened the iron gate with a squeal of hinges.

"Quickly," Jack hissed. "They'll be on us in ...