The tunnel was man-made of more brick and mortar. Someone floated a ball of witchlight ahead of us, bobbing blue over our shoulders to hover just far enough out to light the way. I turned to see Pharo wave at me, and wink.

"Probably best if you don't use your power about now, Tweet," he said. "At least, from what you've told us it may be a bad idea?"

Grateful, I winked back.

The illumination preceded us, leading us deeper. I noticed very quickly the walls turn to ...