Guards! Guards!

the flagstones in the Plaza of Broken Moons, littered here and there with torn bunting, flags, broken bottles and the occasional regurgitated supper. There was still plenty of thunder about, and a green, fresh smell in the air. A few shreds of mist from the Ankh hovered over the stones. It would be dawn soon.
    Vimes’s footsteps echoed wetly from the surrounding buildings as he picked his way across the plaza. The boy had stood here .
    He peered through the mist shreds at the surrounding buildings, getting his bearings. So the dragon had been hovering—he paced forward— here .
    “And,” said Vimes, “this is where it was killed.”
    He fumbled in his pockets. There were all sorts of things in there—keys, bits of string, corks. His finger closed on a stub end of chalk.
    He knelt down. Errol jumped off his shoulder and waddled away to inspect the detritus of the celebration. He always sniffed everything before he ate it, Vimes noticed. It was a bit of a puzzle why he bothered, because he always ate it anyway.
    Its head had been about, let’s see, here .
    He walked backward, dragging the chalk over the stones, progressing slowly over the damp, empty square like an ancient worshipper treading a maze. Here a wing, curving away toward a tail which stretched out to here , change hands, now head for the other wing…
    When he finished he walked to the center of the outline and ran his hands over the stones. He realized he was half-expecting them to be warm.
    Surely there should be something. Some, oh, he didn’t know, some grease or something, some crispy fried dragon lumps.
    Errol started eating a broken bottle with every sign of enjoyment.
    “You know what I think?” said Vimes. “I think it went somewhere.”
    Thunder rolled again.
    “All right, all right,” muttered Vimes. “It was just a thought. It wasn’t that dramatic.”
    Errol stopped in mid-crunch.
    Very slowly, as though it was mounted on very smooth, well-oiled bearings, the dragon’s head turned to face upward.
    What it was staring at intently was a patch of empty air. There wasn’t much else you could say about it.
    Vimes shivered under his cape. This was daft.
    “Look, don’t muck about,” he said. “There’s nothing there.”
    Errol started to tremble.
    “It’s just the rain,” said Vimes. “Go on, finish your bottle. Nice bottle.”
    A thin, worried keening noise broke from the dragon’s mouth.
    “I’ll show you,” said Vimes. He cast around and spotted one of Throat’s sausages, cast aside by a hungry reveller who had decided he was never going to be that hungry. He picked it up.
    “Look,” he said, and threw it upward.
    He felt sure, watching its trajectory, that it ought to have fallen back to the ground. It shouldn’t have fallen away , as if he’d dropped it neatly into a tunnel in the sky. And the tunnel shouldn’t have been looking back at him.
    Vivid purple lightning lashed from the empty air and struck the houses on the near side of the plaza, skittering across the walls for several yards before winking out with a suddenness that almost denied that it had ever happened at all.
    Then it erupted again, this time hitting the rimward wall. The light broke where it hit into a network of searching tendrils spreading across the stones.
    The third attempt went upward, forming an actinic column that eventually rose fifty or sixty feet in the air, appeared to stabilize, and started to spin slowly.
    Vimes felt that a comment was called for. He said: “Arrgh.”
    As the light revolved it sent out thin zigzag streamers that jittered away across the rooftops, sometimes dipping, sometimes doubling back. Searching .
    Errol ran up Vimes’s back in a flurry of claws and fastened himself firmly on his shoulder. The excruciating agony recalled to Vimes that there was something he should be doing. Was it time to scream again? He tried another “Arrgh.” No, probably not.
    The air started to smell like burning tin.
    Lady Ramkin’s coach rattled into the plaza making a noise like a roulette wheel and pounded straight for Vimes, stopping in a skid that sent it juddering around in a semi-circle and forced the horses either to face the other way or plait their legs. A furious vision in padded leather, gauntlets, tiara and thirty yards of damp pink tulle leaned down toward him and screamed: “Come on, you bloody idiot!”
    One glove caught him under his unresisting shoulder and hauled him bodily onto the box.
    “And stop