'I can hardly hear you, the rain's coming down so hard,' he shouted.

'I said I think we have a double bluff here,' Masters told him. 'At first appearance it's quite simple, but no, the more I think about it the more confusing it becomes.'

'Simple?' He could not share the doctor's excitement for the game. It was fine for him; he was warm and dry and safe. Vince just wanted to solve the damned thing and find out what had happened to his friends. His boots were full of water and rain was dripping inside his collar, down his spine.

'This is to do with a set of paintings,' said Masters. 'Hogarth's four famous Times of the Day paintings to be exact, Morning, Noon, Evening and Night. They're right here in London. The problem is, they're absolutely stuffed with allegorical allusions that point in all sorts of different directions. We have too many clues to follow.'

'Couldn't it be simpler than that?' asked Vince, forcing himself to think clearly. 'Surely Sebastian wasn't expecting me to work out the symbolism in paintings at five o'clock in the morning.'

'I think that's precisely what he wants you to do,' replied Masters. 'Don't you see, he's thrusting his preferred kind of education on you, British, classical, old school. And these paintings are games, filled with little puzzles, just the sort of thing he likes.'

'I've seen the Hogarth pictures at the Tate Gallery. Couldn't I be intended to go there?'

'What would be the point of specifying the Hogarth pictures so exactly when any artist exhibited at the Tate would do? And why go into such detail about them? No, the answer has to be in the paintings themselves.'

'Do you have any reproductions of them to hand?'

'I probably have quite a few. They're featured in a great many art volumes. Are you sheltering somewhere out of the wet?'

'No.'

'Listen, you'd better make yourself scarce from there if the police are on their way. It's going to take us a few minutes to locate reproductions of the paintings and examine them. We'll call you back.'

He gave Masters his new number and rang off. With a hiss of exasperation, he stepped back into the drenching downpour.

Louie could feel something cold and wet pressing against him in the icy rushing torrent, something with the heaviness of flesh and bone. It thumped against his burning thigh as the water pounded around him, dragging at his limbs. He reached down into the freezing stream and grabbed a human arm, pulling it nearer. Pam was the worse for wear but still very much alive, and began coughing violently as soon as he raised her head. There seemed to be a stone slab set halfway across the shaft, about two feet down in the water. They were safe so long as they managed to stay on it, as she had; to step off would mean being swept away along the tunnel to who knew where. Forcing one arm around Pam's waist, he used the other to cling to the iron rungs, but had no strength to pull the pair of them free from the churning river.

'Hit my head,' yelled Pam miserably. Louie was so surprised he nearly dropped her. 'Someone let the lid fall on my head. Can't we get out?'

'No, the cover's been put back in place,' he explained. 'Are you strong enough to hold onto something?'

'I think so.'

He gently pushed her through the water to the side wall and wrapped her fingers around the rungs. 'Now hold tight. I'll see if I can get the lid off. Don't let go, whatever you do.'

Slowly, painfully, he climbed the rungs one at a time until his head was level with the top of the shaft. With his free hand he attempted to push the lid free, but there was not even a quarter-inch of movement. His right thigh, where the crossbow dart had entered, felt as though it was on fire. God only knew how many inoculations he would need if they ever got out of here alive.

He stepped down a rung to try and get a better grip, and the aluminium shaft of the dart caught inside one of the ladder struts, causing him to yell out in pain. His fingers closed on air as the rung eluded his grasp, and he fell back. For a moment he lay across the shaft breathing hard, his shoulder against the slime-covered wall opposite. Then as Pam screamed his name he slipped again and fell feet first, bypassing the ledge, into the storm-driven cloacal rage below.

'BUT ARTHUR, we need your knowledge down here,' pleaded Maggie Armitage. 'You still remember all the old, esoteric stuff even I've forgotten.'

'I'm not sure I take that as a compliment,' replied the elderly detective. 'Anyway, there are too many cooks in this room. You need to go over those paintings inch by inch, preferably with a magnifying glass. Someone should be working out what the League of Prometheus is up to.'

'Surely we know that already.'

'No,' said Bryant emphatically, 'that is precisely what we don't know, beyond the fact that Vincent Reynolds is being used. Could their meeting have been prearranged right from the outset, d'you suppose?'

'I don't see how,' answered Masters. 'Vincent says he found Sebastian's name in a magazine.'

'Hmm. Harold, may I borrow your wife?' He extended his hand. 'Jane, you have a lively mind. I know it's late, but you wouldn't mind helping me for a few minutes, would you?'

'Not at all,' replied Jane, flattered. 'What do you want me to do?'

'I'm not a fan of the Internet, as you know. It seems to me rather like the stack of magazines one always finds in dentists' waiting rooms. They cover all the subjects you have no interest in reading about, and the only pages you'd like to read are partially missing. Still, it could be useful in this situation. Harold was telling me that you use it at the museum, and that you have a connection set up here. Can you show me how to locate those page-things?'

'Web-sites, yes, of course. I'll show you where the terminal is.' She led the way upstairs. Unlike his partner John May, who was in the thrall of all things cybernetic, Bryant had no love or understanding of technology. Its usefulness in locating information, however, could not be denied. He needed to probe deeper into the newspaper files for reports of the drowning of Melanie Daniels, and knew that he could probably access all the archival material he needed through the Internet. At the back of his mind was the suspicion that Sebastian had somehow been responsible for the girl's death. Either it was an accident that he had unwittingly caused, or he had actually murdered her in a fit of anger. Suppose Sir Nicholas had discovered the truth, and had refused to help his boy out of the situation? Surely that was reason enough for father and son to become estranged?

And yet this alone was not enough to explain the League's mobilisation in the last few hours. It seemed unlikely that an accident occurring over seven years ago had any bearing on the drama now being played out, but what else did they have to go on? As he seated himself before the console and Jane switched on the modem for him, he realised how little time there was left before the dawn would start shedding its unwelcome light on the events of the night.

'Let's have a good look at these pictures,' said Masters. He adjusted his bifocals and scanned the page. 'We'll take the clues in the order that they were written down. The night of September 3rd and the passing of Proserpine.' He opened a heavy, battered copy of The Works of William Hogarth, bound in brown leather, and located the Times of the Day engravings. The sequence of four ended with Night. 'Well, Proserpine is Persephone, the wife of Hades, the goddess of the underworld…'

'I know a fair amount about these pictures,' said Maggie keenly. 'Hogarth is often cited by our coven members because of his reliance on symbolism and myth. The members like that sort of thing. Look, here, at the Night picture.' She tapped it with a crimson nail. 'It's apparently set in Hartshorn Lane, Charing Cross. The road is long gone, of course. The oak boughs on the sign and the oak leaves in the freemason's hat suggest the date – May 29th, the anniversary of Charles the Second's restoration. There's a crashed coach in the bottom right-hand corner. I think it's meant as a sort of nasty parody of Persephone bringing on the night. Most of Hogarth's jests have a sadistic edge created by his love of paradox. There's another joke in the surrounding scene – rather than preparing for bed, everyone is getting ready to go out.'