Enraged, she pulled on her dressing gown, and moments later she found herself in the street, marching towards the church. She couldn't remember coming down the stairs, or pushing open the front door. All she felt was an anger at the injustice, that these hooligans might escape punishment.

'Now, listen here!' she shouted as the two young people dropped down on to the ground. It was a girl and a boy. She thought she recognised the lad, but it was difficult to be sure in the semidarkness. 'Just what do you think you're doing?'

Her voice was loud enough, she supposed, to wake even her corpse-like husband.

The two vandals fled in opposite directions. 'Run!' shouted the unfamiliar girl as she pa.s.sed.

Megan Tyley stood, rooted to the spot, her mouth hanging open. The girl had been telling her her to run. to run.

Something brushed against Megan's back, and she turned.

A hulking, unreal figure was patrolling the shadows around the church wall. Its dirty, striped clothes were covered with leaves and stalks of straw.

The misshapen, lumpy head twisted uncertainly in her direction. It could have been a pumpkin covered in cloth, with a harsh red slit for a mouth, were it not for the eyes, deep within the face.

Frightened, powerless eyes. Eyes that had once been human. Eyes that cried out silently - Mum.

'I don't get it,' said Hill, reading the page in his hand again.

'This is just... nothing.'

'On the contrary,' said the Doctor. 'It establishes a link.'

'What link?'

The Doctor took the paper from Hill's hand. 'This letter acknowledges an invoice for construction work carried out by one of Shanks's companies at the local water company's purification plant at the Garside reservoir.'

'So?' asked Hill.

'Look at the board of directors for Mersey Water PLC,' noted Denman with a triumphant snarl. 'Significant, wouldn't you say?'

'Matthew Hatch - non-executive director,' read Hill. 'I still don't see anything to get excited about, sir. Hatch has put some work Shanks's way. So what? We know they're mates.

At worst we've got a bit of bribery and corruption - which we'd never be able to prove. We might wreck Hatch's political career, but Shanks is still fireproof.'

'n.o.body's fireproof,' said Denman angrily.

'Gentlemen,' the Doctor said. 'You're all missing the point.

Why do Shanks and Hatch have an interest in the city's water supply?'

'I don't know. It's not what I'd expect of Shanks,' said Denman. 'What's he playing at?'

'I'm not entirely sure,' admitted the Doctor. 'But I have some very horrible suspicions. I know that Shanks has scientists working for him, and they're not just developing narcotics. I suggest we take a look at that reservoir.'

They drove in near silence across the city. The sun was rising and the streets were filling with commuters. A main road took them through rolling countryside. Twenty minutes beyond Liverpool they saw the first road sign for Garside.

The car came to halt overlooking the reservoir, an enormous construction of swept white concrete. The sun was a ball of orange, floating on the still waters.

Denman rummaged around in the glove box, and found a small pair of binoculars. He scanned the purification plant on the other side of the reservoir, a simple block of a building, surrounded by fences. 'There's a Jag there,' he announced.

'It's Shanks's.'

'Are you sure?' queried Hill.

'It's my business to know,' said Denman.

The Doctor pushed open the door. 'We should find out what Shanks is up to.'

Hill, in the driving seat, turned to Denman. 'But Mr Savage said -'

'I don't care,' snapped Denman. 'If you want to arrest me when I come out of that building, you can. But I'm going to have that piece of vermin.' He got out of the car. 'If we're not out in half an hour, call for backup.'

Straggling pine trees had been planted in a strip around one bank of the reservoir. The Doctor and Denman kept to the shadowy undergrowth as they approached the building.

Shanks's Jaguar was just visible through a razor-wire-topped fence. A thick metal gate bore the Mersey Water Company's logo.

The Doctor and Denman skirted around to the back of the purification plant. An ancient deciduous wood terminated just short of the building. The bough of one particular tree extended over the fence. With surprising agility, the Doctor climbed up into the branches of the oak, stopping occasionally to give the puffing Denman a hand. Then, with great care, his feet dangling down on either side, the Doctor edged his way along the bough. He crossed the line of the fence, and began to lower himself towards the ground.

He dropped down, tumbling on to his side like a parachutist. Denman followed.

The two men walked across the weed-covered patch of land towards what appeared to be a fire exit. Denman raised his boot, ready to kick down the door.

'Oh, I think we can do better than that,' said the Doctor. 'A piggyback, if you don't mind?'

'Doctor, I didn't come all this way to muck about with -'

'A piggyback, please,' said the Doctor sharply. 'Or would you rather set off all the alarms inside this building?' He pointed. Above the door was a small box of white Perspex with an integral loudspeaker. Thick, insulated wires ran from that down to sensors on the door and frame, and back into the building.

The Doctor found a flat piece of flint on the ground, and then gingerly clambered up Denman's broad back.

'Oh, do keep still,' said the Doctor.

'I'm trying my best,' said Denman, swaying under the Doctor's weight.

The Doctor removed a couple of screws, revealing a simple red light bulb and a more complex box of electronics.

'If a fire breaks out,' said the Doctor, 'all these alarms are triggered. Lights flash, klaxons wail - and the doors automatically unlock themselves. It goes without saying that you can open these exits manually from the inside, but seeing as we're not, and -'

'Get on with it,' snapped Denman.

'So,' said the Doctor, 'what we've got to do is trigger the circuit that will open this door without setting off the actual alarm.' He rummaged through his pockets, and found a small spool of bare electrical cable. He bent a complex shape from the wire, and began gingerly inserting it into the fire sensor.

'And now something that doesn't conduct electricity...' He pressed a small black coat b.u.t.ton against a switch.

There was a loud click from the door.

'Et viola,' said the Doctor, moments before falling to the ground as Denman finally let go. said the Doctor, moments before falling to the ground as Denman finally let go.

'Let's find Shanks,' said the big policeman, pushing his way through the door.

'No,' said the Doctor, brushing himself down with as much dignity as he could muster. 'Let's find out what he's up to first.'

'Which is?'

'Well,' said the Doctor. 'I think it will involve water, don't you?' And he swept past Denman and into the building.

They made their way towards the main purification and testing room. It was a functional construction of brick and metal, and contained a large number of circular tanks, connected by a complex array of thick tubing. A feint smell of ozone hung in the air. The place was deserted.

'What are we looking for?' asked Denman.

'Something that doesn't belong,' said the Doctor, scanning the room with expert detachment. 'There,' he announced at last, pointing to a gantry high up in the ceiling. A metal vat had been bolted on to an observation walkway, a twisted black rubber hose leading down into the water.

The Doctor made his way up the wrought-iron steps two at a time, Denman close behind. The walkway, slatted to reveal the tanks and the floor far below, swayed slightly as the two men approached the container. Between the vat and the tube was a small electronic box, a row of LEDs on the front. 'It's releasing a very precise amount of fluid straight into the water supply,' explained the Doctor. 'After this tank, it heads straight to the taps and toilets of Merseyside.'

Denman looked at the cylinder. 'It isn't very big,' he said.

'Surely it can't do much harm?'

'If it were a concentrated poison, it could kill thousands, even if diluted to one part per billion.' The Doctor noticed Denman's horrified expression. 'But I don't think this is poison. Even Shanks has little to gain from wholesale slaughter.'

'That's true,' said a voice, unexpectedly close.

Denman and the Doctor turned, and Shanks emerged from a shadowy area at the far end of the gantry. 'Took your time, lads,' he said as he walked towards them, a pistol held confidently in his right hand.

'You knew we'd come?' the Doctor asked, with a hint of resignation in his voice.

'Oh yeah. I've had someone watching you. And that office you broke into is riddled with sensors. You tripped so many of them the security desk looked like a Christmas tree.' He turned to face Denman. 'I'm sorry to hear about your kid,' he said. 'So unexpected.'

Denman snarled, about to hurl himself at the gangster, but Shanks pointed the gun straight at him.

The Doctor stared at Shanks.

'I'm nothing special.'

'Oh yes you are. You're very important. And that's the most frightening thing in the world.' frightening thing in the world.'

The Doctor shook his head, remembering how the sun had risen, all those years ago, in Hexen Bridge. 'Are you satisfied?' he asked. 'You're important now. You can end a man's life simply by giving orders.' His eyes burnt with disappointment, and Shanks glanced away momentarily. 'I hope you're pleased with yourself.'

'What's in the container?' asked Denman, through gritted teeth.

'Something Hatch's crowd have concocted,' said Shanks. 'It immunises people against CJD. Means they can go on munching burgers in patriotic safety.'

'I've heard no official announcement,' said Denman.

'Of course not, you divvy. This is all hush-hush.' Shanks tapped the canister with his gun. 'People are still so twitchy about BSE, Matt said it would take years to get this stuff pa.s.sed.'

'So you're pumping it straight into the water supply, so that you can try it out on the populace?' queried the Doctor.

'That's obscene,' said Denman.

Shanks shook his head. 'You could say I'm putting something back into the community after all these years.' He smiled. 'I always told you I had a compa.s.sionate side.'

'Don't give me that c.r.a.p,' said Denman.

'Funny you should mention that,' said Shanks. 'I was thinking of dumping you both in the sewage.' His eyes became cold and almost colourless. 'I can't think of a worse way to go.'

'I don't believe a word of it,' said the Doctor suddenly.

'What?' said Shanks.

'This tank doesn't contain a cure for Creutzfeldt-Jakob disease,' stated the Doctor firmly.

For the first time, Shanks looked ill at ease. 'That's what Matt told me.'

'And you believed him,' mocked Denman. 'I reckon he's been stringing you along all this time, Shanksy.'

'Don't call me that!' snapped Shanks, his expression revealing the shabby child, once scorned and still lonely, beneath the adult veneer.