Daniel probed into the linen bag and got a smudge of the stuff on his fingertips. The answer was obvious. 'This is much finer than that in the keg.' And that was the clew that reminded him where he had seen such a bag before. The night that Roger Comstock had blown himself up in the laboratory, he had been grinding gunpowder very fine, and pouring it into a bag just like this one. 'Where did this come from? A theatre?'