Turning off their flashlights so as not to be easy targets, Matt, Sergeant Gupta, and Constable Spencer Sutcliffe slipped through the opening. They had no sooner entered than the stone-wall-door behind them slammed shut.

“That was unexpected,” complained Matt. “Is that likely to cause a problem for the others?”

“Not likely,” whispered Spencer. “Unless…”

“Unless what?” Matt asked, not hiding his sudden concern.

“Un...