Thud!

Ankh-Morpork.
    A clue.
    She smiled in the dwindling darkness. And the trouble with clues, as Mister Vimes always said, was that they were so easy to make. You could walk around with a pocket full of the bloody things.
    The darkness was disappearing because the light was growing. Angua looked up.
    There was a huge, bright symbol on the wall where Carrot had touched it. He dragged some meat across it, she thought. They’ve turned up for the feast…
    Ardent came back in, with Helmclever trailing after him.
    He got as far as: “The door here can be opened again but, alas, we—” and stopped.
    They were happy vurms. By the standards of greeny-white glow, they were brilliant.
    Behind Carrot there was now a gently glowing circle, with two diagonal lines slashed through it. Both dwarfs stared at it as if in shock.
    “Well, let’s take a look, shall we?” said Carrot, apparently oblivious to all this.
    “—we, alas, the water…water…not entirely watertight…the other doors…the troll caused flooding…” Ardent murmured, not taking his eyes off the glow.
    “But you say we can go through here, at least?” said Carrot politely, pointing to the sealed door.
    “Er…yes. Yes. Certainly.”
    The steward hurried forward and produced a key. The wheel, unlocked, turned easily. Angua was acutely aware of how the muscles on Carrot’s bare arms glistened and pumped as he pulled the metal door open.
    Oh no, not yet , surely! She ought to have at least another day! It was the vampire, that’s what it was, standing there looking so innocent. Bits of her body wanted her to become a wolf, right now, to defend herself…
    There was a pillared room on the other side of the door. It smelled damp and unfinished. There were vurms on the ceiling, but the floor was muddy and squelched underfoot.
    Angua could make out another dwarf door across the room, and there was one on either side as well.
    “We take spoil to a heap on the waste ground outside,” said Ardent. “We, er, believe the troll got in that way. It was an unpardonable oversight.” He still sounded uneasy.
    “And the troll was not seen?” said Carrot, kicking at the mud.
    “No. These chambers are finished. The diggers are elsewhere, but they came as soon as they could. We believe the grag had come up here for solitude. To die at the random hand of an abomination!”
    “Lucky for the troll, wasn’t it, sir?” said Angua sharply. “He just happened to wander in and stumble across Hamcrusher?”
    Carrot’s boot struck something metallic. He kicked some more mud away.
    “You’ve laid rails?” he said. “You must be shifting a lot of spoil, sir.”
    “Better to push than to carry,” said Ardent. “Now, I have arranged for—”
    “Hold on, what’s this?” said Carrot. He squatted down and pulled at something pale. “It’s a piece of bone, by the look of it. On a string.”
    “There are plenty of old bones,” said Ardent. “Now, I—”
    It came free with a gloop , and grinned at them in the sickly light.
    “It doesn’t look very old, sir,” said Carrot.
    Just one breath was enough for Angua.
    “It’s a sheep skull,” she said. “About three months dead.” Oh, another clue, she added to herself. Nice and convenient for us to find, too.
    “Could have been dropped by the troll,” said Carrot.
    “A troll?” said Ardent, backing away.
    It wasn’t the reaction Angua had expected. Ardent had been nervous already, but now, under all those wrappings, he was on the verge of panic.
    “You did say a troll had attacked the grag, sir?” said Carrot.
    “But we never—I never saw that before! Why didn’t we find it? Did it come back?”
    “All the doors are sealed, sir,” said Carrot patiently. “Aren’t they?”
    “But have we sealed it in here with us?” It was practically a shriek.
    “You’d know, sir, wouldn’t you?” said Carrot. “Trolls sort of, well, stand out.”
    “I must fetch guards!” said Ardent, backing away toward the single open door. “It could be anywhere!”
    “Then you could be heading right toward it, sir ,” said Angua.
    Ardent stopped dead for a moment, and then uttered a little whimper and ran into the dark, Helmclever on his heels.
    “Well, how do we all think that went?” said Angua, with a horrible smile. “And what was that you said to him in dwarfish…‘You know I am a dwarf in the brotherhood of all dwarfs’?”
    “Erm, ‘With emphatic certainty you know me. I observe the rites of the