There were footprints in the mud.

“How long have you lived here?” said Cuddy, suddenly feeling very conspicuous in the middle of the tunnel.

“Nine-er years. That is the number of years I have lived here. Nine-er,” said Detritus, proudly. “It only one of a large… number of numbers I can count to.”

“Have you ever heard of tunnels under the city?”

“No.”

“Someone knows about them, though.”

“Yes.”

“What shall we do?”

The answer was inevitable. They'd chased a man into the pork futures warehouse, and nearly died. Then they'd ended up in the middle of a small war, and nearly died. Now they were in a mysterious tunnel where there were fresh footprints. If Corporal Carrot or Sergeant Colon said, “And what did you do then?”, neither of them could face up to the thought of saying “We came back.”

“The footprints go this way,” said Cuddy, “and then they return. But the ones coming back aren't so deep as the ones going. You can see they're later ones because they're over the top of the other ones. So he was heavier going than he was coming back, yes?”

“Blight,” said Detritus.

“So that means…?”

“He lose weight?”

“He was carrying something, and he left it… up ahead somewhere.”

They stared at the darkness.

“So we go and find what it was?” said Detritus.

“I think so. How do you feel?”

“Feel OK.”

Different species though they were, their minds had focused on a single image, involving a muzzle flash and a lead slug singing through the subterranean night.

“He came back,” said Cuddy.

“Yes,” said Detritus.

They looked at the darkness again.

“It has not been a nice day,” said Cuddy.

“That the truth.”

“I'd just like to know something, in case… I mean… look, what happened in the pork store? You did all that maths! All that counting!”

“I… dunno. I saw it all.”

“All what?”

“Just all of it. Everything. All the numbers in the world. I could count them all.”

“What did they equal?”

“Dunno. What does equal mean?”

They trudged on, to see what the future held.

The trail led eventually into a narrower tunnel, barely wide enough for the troll to stand upright. Finally they could go no further. A stone had dropped out of the roof and rubble and mud had percolated through, blocking the tunnel. But that didn't matter because they'd found what they were looking for, even though they hadn't been looking for it.

“Oh dear,” said Detritus.

“Very definitely,” said Cuddy. He looked around vaguely.

“You know,” he said, “I reckon these tunnels are usually full of water. They're well below the normal river level.”

He looked back to the pathetic discovery.

“There's going to be a lot of trouble about this,” he said.

“It's his badge,” said Carrot. “Good grief. He's holding it so tight it's cut right into his hand.”

Technically Ankh-Morpork is built on loam, but what it is mainly built on is Ankh-Morpork; it has been constructed, burned down, silted up, and rebuilt so many times that its foundations are old cellars, buried roads and the fossil bones and middens of earlier cities.

Below these, in the darkness, sat the troll and the dwarf.

“What we doing now?”

“We ought to leave it here and fetch Corporal Carrot. He'll know what to do.”

Detritus looked over his shoulder at the thing behind them.

“I don't like that,” he said. “It not right to leave it here.”

“Right. Yes, you're right. But you're a troll and I'm a dwarf. What do you think would happen if people saw us carrying that along the streets?”

“Big trouble.”

“Correct. Come on. Let's follow the footprints back out.”

“Supposing it gone when we come back?” said Detritus, lumbering to his feet.

“How? And we're following the tracks out, so if whoever it was who put it there comes back, we'll run straight into them.”

“Oh, good. I glad you said that.”

Vimes sat on the edge of his bed while Angua bandaged his hand.

“Captain Quirke?” said Carrot. “But he's… not a good choice.”

“Mayonnaise Quirke, we used to call him,” said Colon. “He's a pillock.”

“Don't tell me,” said Angua. “He's rich, thick and oily, yes?”

“And smells faintly of eggs,” said Carrot.

“Plumes in his helmet,” said Colon, “and a breastplate you can see your face in.”

“Well, Carrot's got one of those too,” said Nobby.

“Yes, but the difference is, Carrot keeps his armour polished because he… likes nice clean armour,” said Colon loyally. “While Quirke keeps his shiny because he's a pillock.”

“But he's wrapped up the case,” said Nobby. “I heard about it when I went out for the coffee. He's arrested Coalface the troll. You know, captain? The privy cleaner. Someone saw him near Rime Street just before the dwarf got killed.”

“But he's massive,” said Carrot. “He couldn't have got through the door.”

“He's got a motive,” said Nobby.

“Yes?”

“Yes. Hammerhock was a dwarf.”

“That's not a motive.”

“It is for a troll. Anyway, if he didn't do that, he probably did something. There's plenty of evidence against him.”

“Like what?” said Angua.

“He's a troll.”

“That's not evidence.”

“It is to Captain Quirke,” said the sergeant.

“He's bound to have done something,” Nobby repeated.

In this he was echoing the Patrician's view of crime and punishment. If there was crime, there should be punishment. If the specific criminal should be involved in the punishment process then this was a happy accident, but if not then any criminal would do, and since everyone was undoubtedly guilty of something, the net result was that, in general terms, justice was done.

“He's a nasty piece of work, that Coalface,” said Colon. “A righthand troll for Chrysoprase.”

“Yes, but he couldn't have killed Bjorn,” said Carrot. “And what about the beggar girl?”

Vimes sat looking at the floor.

“What do you think, captain?” said Carrot.

Vimes shrugged.

“Who cares?” he said.

“Well, you care,” said Carrot. “You always care. We can't let even someone like—”

“Listen to me,” said Vimes, in a small voice. “Supposing we'd found who killed the dwarf and the clown? Or the girl. It wouldn't make any difference. It's all rotten anyway.”

“What is, captain?” said Colon.

“All of it. You might as well try and empty a well with a sieve. Let the Assassins try to sort it out. Or the thieves. He can try the rats next. Why not? We're not the people for this. We ought to have just stayed with ringing our bells and shouting ‘All's well!’”

“But all isn't well, captain,” said Carrot.

“So what? When has that ever mattered?”

“Oh, dear,” said Angua, under her breath. “I think perhaps you gave him too much of that coffee…”

Vimes said, “I'm retiring from the Watch tomorrow. Twenty-five years on the streets—”

Nobby started to grin nervously and stopped as the sergeant, without apparently shifting position, grabbed one of his arms and twisted it gently but meaningfully up his back.

“—and what good's it all been? What good have I done? I've just worn out a lot of boots. There's no place in Ankh-Morpork for policemen! Who cares what's right or wrong? Assassins and thieves and trolls and dwarfs! Might as well have a bloody king and have done with it!”

The rest of the Night Watch stood looking at their feet in mute embarrassment. Then Carrot said, “It's better to light a candle than curse the darkness, captain. That's what they say.”

“What?” Vimes' sudden rage was like a thunderclap. “Who says that? When has that ever been true? It's never been true! It's the kind of thing people without power say to make it all seem less bloody awful, but it's just words, it never makes any difference–”