Angua looked at some of the other dogs. They were all unkempt. They were also, in a strange way, un-doglike. There was a small and rather dainty white poodle that still just about had the overgrown remains of its poodle cut, and a lapdog with the tattered remains of a tartan jacket still hanging from its shoulder. But they weren't milling around, or squabbling. They had a uniform intent look that she'd seen before, although never on dogs.

Gaspode was clearly trembling now. Angua slunk over to the poodle. It still had a diamante collar visible under the crusty fur.

'This Big Fido,' she said, 'is he some kind of wolf, or what?'

'Spiritually, all dogs are wolves,' said the poodle, 'but cynically and cruelly severed from their true destiny by the manipulations of so-called humanity.'

It sounded like a quote. 'Big Fido said that?' Angua hazarded.

The poodle turned its head. For the first time she saw its eyes. They were red, and as mad as hell. Anything with eyes like that could kill anything it wanted because madness, true madness, can drive a fist through a plank.

'Yes,' said Big Fido.

He had been a normal dog. He'd begged, and rolled over, and heeled, and fetched. Every night he'd been taken for a walk.

There was no flash of light when It happened. He'd just been lying in his basket one night and he'd thought about his name, which was Fido, and the name on the basket, which was Fido. And he thought about his blanket with Fido on it, and his bowl with Fido on it, and above all he brooded on the collar with Fido on it, and something somewhere deep in his brain had gone 'click' and he'd eaten his blanket, savaged his owner and dived out through the kitchen window. In the street outside a labrador four times the size of Fido had sniggered at the collar, and thirty seconds later had fled, whimpering.

That had just been the start.

The dog hierarchy was a simple matter. Fido had simply asked around, generally in a muffled voice because he had someone's leg in his jaws, until he located the leader of the largest gang of feral dogs in the city. People – that is, dogs -still talked about the fight between Fido and Barking Mad Arthur, a rottweiler with one eye and a very bad temper. But most animals don't fight to the death, only to the defeat, and Fido was impossible to defeat; he was simply a very small fast killing streak with a collar. He'd hung on to bits of Barking Mad Arthur until Barking Mad Arthur had given in, and then to his amazement Fido had killed him. There was something inexplicably determined about the dog – you could have sandblasted him for five minutes and what was left still wouldn't have given up and you'd better not turn your back on it.

Because Big Fido had a dream.

'Is there a problem?' said Carrot.

'That troll insulted that dwarf,' said Stronginthearm the dwarf.

'I heard Acting-Constable Detritus give an order to Lance-Constable . . . Hrolf Pyjama,' said Carrot. 'What about it?'

'He's a troll!'

'Well?'

'He insulted a dwarf!'

'Actually, it's a technical milit'ry term—' said Sergeant Colon.

'That damn troll just happened to save my life today,' shouted Cuddy.

'What for?'

'What for? What for? 'Cos it was my life, that's what tor! I happen to be very attached to it!'

'I didn't mean—'

'You just shut up, Abba Stronginthearm! What do you know about anything, you civilian! Why're you so stupid? Aargh! I'm too short for this shit!'

A shadow loomed in the doorway. Coalface was a basically horizontal shape, a dark mass of fracture lines and sheer surfaces. His eyes gleamed red and suspicious.

'Now you're letting it go!' moaned a dwarf.

'This is because we have no reason to keep him locked up,' said Carrot. 'Whoever killed Mr Hammerhock was small enough to get through a dwarf's doorway. A troll his size couldn't manage that.'

'But everyone knows he's a bad troll!' shouted Stronginthearm.

'I never done nuffin,' said Coalface.

'You can't turn him loose now, sir,' hissed Colon. 'They'll set on him!'