ran around it, and carried on to a point about six inches above the water. Slowly, it widened as the stone slid away into a recess. A few moments later the rumbling stopped and they were peering at a pitch-black rectangle the width of Philip's shoulders. They shone their torches into the opening, and in patches the blackness gave way to reveal stone walls receding into a featureless void beyond.
Laura stepped into the opening, shining her torch around and above her head. The ceiling arched several feet above her. Philip followed, and they both straightened up.
Laura sighed with relief. 'God, that was even harder than I thought it would be.'
'Ought to be grateful you're not six-two …' Philip stopped mid-sentence as the rumbling sound began again. They whirled round to see the stone begin to slide back into place. Philip reacted with surprising speed. Picking up a large rock, he thrust it into the opening. But the door kept on and the rock crumbled.
Laura felt a tremor of panic.
'I think it's OK,' Philip said as reassuringly as he could. He played his torch beam along the walls, which were surprisingly dry. 'The air is fresher here than it was in the stream. And at least we have some headroom. Come on.'
He edged forward slowly, scanning the floor and the walls as he went and brushing aside the cobwebs. The darkness was terrifying and it was taking all his concentration to hold down the unnamed things that his imagination was trying to dredge up to the surface. To stay focused, Philip studied the walls and the limited universe illuminated by the light from his torch. Laura was immediately behind him and she had gripped his hand. He could hear her breathing.
The walls were smooth and much drier than in the Trill Mill Stream tunnel. The smell now was more musty and earthy; the odour of rotting garbage and mould had been left behind. Philip picked his way very carefully. Anything could lie ahead of them a hole in the floor, a mantrap, any number of dangers. The biggest mistake would be to get overconfident. They had to take their time and watch where they stepped, he thought to himself.
The tunnel seemed to go on and on, unchanging. It was about ten feet wide, the walls curved and quite featureless. The floor was compacted soil, dry and flat. Then, suddenly, the tunnel opened out so that the beams from their torches produced only dispersed puddles of faint light on the walls to left and right. Taking a few more paces forward, they realised that they had entered a circular expanse.
'What's that?' Laura shone her torch at a point on the nearest wall at about head height. It revealed a small metal bracket extending from the wall and atop it was an old cream-coloured candle half burned down. Philip ran the beam of his torch along the wall to left and right and they caught sight of several more candles placed at intervals of about ten feet.
'You think they'll still work?' Laura asked.
'Only one way to find out,' Philip replied. 'Matches are in the left-hand back pocket of the rucksack.'
Laura struck one and stood on tiptoe to light the nearest candle. It spluttered and sparked for a few seconds before catching to produce a steady yellow flame. A few moments later they had twenty or more candles alight.
It was only then that they could fully appreciate the size of the chamber. But more importantly, the light from the candles revealed decorations on the floor, on the walls and on the ceiling. The inside of the room was covered with elaborate images. Across the ceiling ran a picture of a huge white stag, its antlers at least ten feet long. Around it other animals leaped and danced. A wolf skulked close to the bottom of the domed ceiling while a flock of birds — giant golden eagles — emerged from the rim of the ceiling to hover over the stag. And around the perimeter ran a fresco depicting a menagerie of creatures all painted in rich colours: ambers, crimsons, ochre and the richest, most royal blue.
Around the walls ran streams of alchemical symbols of different sizes, painted in silver and gold. Some were as tall as a man, running from the floor halfway to the ceiling, others were crowded tight and small. On the circular floor, some forty feet across, was one single image — of five robed maidens holding aloft a bowl containing the sun.
Philip lowered his rucksack to the ground and walked slowly around the room, touching the symbols before squatting down to study the image on the floor. Laura sat on the floor in the centre of the chamber and stared up at the ceiling.
'It's absolutely incredible,' she said after a few moments.
'It's like something out of
'And to think probably only a handful of people have ever seen this.'
'And less than a hundred feet above our heads buses are running along St Aldates.'
'What do you think it's for?' Laura mused.
Philip shrugged. 'I guess it is — was — a meeting place for the Guardians. What do you think?'
But she had just noticed something. 'Look,' she said, 'there's a door.'
It had been easy to miss because there was little more than an outline in the stonework.
Philip pulled out the Newton photocopy. 'This must be the entrance to the labyrinth itself,' he said.
Laura turned to look at the manuscript.
'Here is the passageway that led from the wine cellar of Hertford College.' Philip ran a finger from the foot of the page up to a doorway that joined a complex tangle of interlinking lines; 'We've come in a different way because the old tunnel was sealed off. The Guardians must have built this room after 1690.1 reckon that behind this door we'll be at this point here… and beyond that must be the labyrinth.'
'But first we have to open it.' Laura bent down to examine the symbols in front of her. Philip loosened the catches of his rucksack and pulled out their boots. He sat down and pulled off his waders. Laura removed hers but was concentrating on the markings around the door. Philip then handed her a pair of boots. She slipped them on and laced them up without even looking at what she was doing.
'It's the Guardian statement ALUMNUS AMAS SEMPER UNICUM TUA DEUS: 'Adept, love always thy God,'' she said, pointing to a single sentence among the collection of symbols and illustrations.
'And what's this?' Philip said, pointing to a small aperture that curved upwards into the doorway like a tiny chimney. He lowered himself almost to the floor and looked inside. 'It's full of cobwebs but there's a row of what look like coloured pulleys.'
'Let me see.' Laura crouched down and brushed the cobwebs aside with her torch. She counted ten brightly coloured tags.
'They must be linked with the colours in Charlie's code — the colour changes that the alchemists followed,' Philip said.
Laura reached in and gripped the black tag halfway along the row. It was made from very soft leather. She pulled. It came towards her easily, then clicked into place a foot down from its original position. She looked up at Philip and raised an eyebrow. 'Well, nothing's exploded.'
'Yet. .' he retorted. 'Try the others — white, yellow, red.'
She followed the sequence, pulling down the white tag, then the yellow. Finally her fingers tightened around the red leather strip and she gave it a gentle tug. There was a hollow click. But nothing happened.
Laura got to her feet as Philip picked up the rucksack and kicked the waders away from the door. For several moments nothing happened, then they heard a creaking sound. It grew louder and they stepped back as the stone slab pivoted into the room, revealing a black hole beyond.
'Here we go,' Philip said.
Immediately inside the doorway, they saw two ancient-looking wood-and-rag torches in wall brackets. Laura reached for her matches. The old torches cast a poor light and the electric flashlights were still needed to dispel the gloom. Philip took a cautious step forward.
They were in another stone-walled room, but it was much smaller than the chamber they had just left; and this one was rectangular and low-ceilinged. Directly ahead stood an archway draped in massive cobwebs. They trained their torch beams on the opening. Beyond it a corridor fell away into the darkness. Two feet ahead of them, the floor of the room simply disappeared. Laura gasped and Philip gripped her arm.
'Wow,' she said.
They directed their torches towards the gaping hole. A chasm at least twenty feet across, it took up most of the room. On the far side there was another two-foot-wide platform before the archway, and to left and right the hole stretched to the walls of the chamber. It was a yawning black pit, the bottom invisible. But as their eyes
