But the man and the girl were already pelting down the tunnel, to leave the prisoner alone with his solitude and his despair.

"What is it?" April hissed when they were out of earshot. "How...?"

"Old air shaft I suddenly remembered," Ernie panted as he ran. "The smugglers had to put it in... otherwise things went bad... kept their food and provisions there."

"But, Ernie..." The girl dragged him to a halt. "If we have to go all the way back, and then return on the surface to find your shaft in the dark — we'll never make it. You know it took us fourteen minutes just to get here."

He was already running again. "'Course not... There's a way out just round the corner here... if I remember rightly..."

There were eight and a quarter minutes left when they burst out of a clump of bushes and felt the cool night wind on their cheeks. Stars pricked the sky overhead, but the moon had disappeared behind a bank of cloud to the west. Immediately above them, red Lamps glared fiercely two hundred feet from the ground. Farther down the slope of the moor, lighted windows marked the site of a clump of low buildings.

"Good heavens!" April breathed. "This is the main mast. Do the military people know there's a warren of passages with an exit inside their closely-guarded perimeter?"

"Reckon not," the boy chuckled. "But I guess that's how our friend reached a lot of his secrets. How much time now?"

"Seven and a half," she reminded him urgently.

"Should be in the middle of that patch of furze over there no, not this one: the one just beyond that boulder!

"Watch out!... Ah! Ernie was right!... Here we are, my beauty..."

He was holding aside a branch of gorse and staring with evident delight at what April at first thought was a large rabbit hole.

"There?" she asked incredulously. "Down there?"

He nodded. "Slants down at an angle of forty-five degrees. If we go feet first, and the grating's as insecure as I remember, I may be able to push it out into the room with my heels and then we can drop through. You'm best take off that sheep skin: the shaft's only eighteen inches square...

There were six minutes left before the hourglass was exhausted and Wright's contraption blew them all sky high when April lowered herself into the burrow after the boy and began wriggling downwards on her back. Of all the under ground journeys she had undergone that night, the twenty-odd feet of the slanting airshaft was immeasurably the worst. For the first few feet, dust, wet earth, pebbles and nameless things that moved were all about her face, threatening to suffocate her. After that, the conduit was carved in the solid rock and she was aware of nothing but coldness, damp, hardness, and the remorseless pressure of thousand of tons of earth, the thickness between her and the man-made steel structure which might at any minute, with her and the earth and the man bound in the cell somewhere below them, go howling skywards in a million fragments. At any minute? In four and a quarter minutes, to be precise.

The passage became so narrow that she could no longer raise her hands from her sides; they were pinioned as effectively as if she had been in a straightjacket. The darkness was total and absolute, the air stuffing, in the two inches of black space between her nose and the wet rock. And she couldn't take a deep breath because the rock pressed too closely upon her ribs for her to inflate her lungs. She couldn't move back upwards because she had no purchase; all she could do was to inch down into the after the scrabbling noises and gasping breaths that were Ernie.

Four minutes.

Suppose they got stuck? Suppose the shaft had become choked? She dared not speak to him: breath was too precious. But suppose — she put the thought from her. And then, lying on her back in this sightless and speechless black burrow, her feet struck something hard. She could go no farther. Her heels had come up against Ernie's shoulders. He was stuck.

The shaft was wide enough now for her to raise one hand up across her chest. Scraping the knuckles on the rook, she peered at the luminous dial of her wristwatch.

Three and a quarter minutes.

She bit back a sob of despair. What had happened? Why didn't he move? And then he did... There was a great bursting, clanging, ringing noise... and a rush of air and a flooding of light and the feel of his shoulders against her soles had gone. And then she was falling.

And suddenly she struck the flagged floor of a room with a jar, and a shower of dust and small stones followed her from the dark hole opening in the wall above and behind her.

Mark Slate was sitting in an iron chair cemented to the floor. His lips were swollen and cracked. He had a black eye. There were ugly bruises on his face. His jacket was torn and there were three thin streams of dried blood across his shirt front. The ankles and wrists wired to the chair were purple from loss of circulation.

"My God!" he croaked through puffy lips. "What happened to you?"

April looked at herself and laughed hysterically. Her knees showed through her trousers, her sweater was ripped, there was mud in her hair, and she was covered all over in green slime from the Keg-Hole. Apart from which her boots were rimed with salt and her face was bleeding from half a dozen small cuts. "Excuse me," she said. "I didn't bother to dress."

Ernie was staring at the complexity of wires and valves and detonators surrounding a huge hour glass in a wooden stand, from the top half of which the pepper-and-salt grains of sand were silkily pouring. On the dwindling remnant of sand spiral ling towards the hole, a tiny square of metal attached to a hair-thin wire was riding.

"Ernie!" she almost screamed. "I know a bit about explosives — but the complexity of that defeats me! I'd have to trace back... I couldn't... I mean we can't release him and go — and we've only got... we've only got a minute and a half..."

The boy looked up. He was smiling. "Not to worry," he said. "I'm not as young as I look, you know. I did my military service — in the Sappers, as a matter of fact. I was in a special unit... Bomb disposal!"

CHAPTER FIFTEEN: A DEAD LIBERTY!

"The one thing I don't really get," Mark Slate said two days later, "is the bit about the burglaries. If Sheila Duncan was a double agent, knowingly passing on microfilm to THRUSH couriers who called for it at her booth, and if she was killed because they found out she also worked for us, then I still can't see why they had to break in. What were they after?"

"The last roll of film delivered to her," April said. "They wanted it back." They were in the Matra-Bonnet, speeding along the empty roads between Porthallow and Falmouth on their way back to London. It was warmer and the sun was shining.

"You mean it hadn't been collected? Nobody had asked for a pixie in Porphyry and been given a lighthouse instead?"

"No, that's just the point. When he killed her, Wright found nothing and assumed it had already been collected. But then when an agent came — and after him another — and neither burglaries nor enquiries did the trick, then they reported to their controls, and it filtered back to Wright. So he sent his wife to ask, and when she drew blank, burgled the place again to see if he could discover where she'd hidden the film."

"So it was Wright we chased that night?"

"Yes. He did the break-in while Mason and Jacko manoeuvred poor Harry Bosustow on to Wright's boat and murdered him."

"That Jacko!" Slate said ruminatively, massaging his chin and shaking his head. "No wonder he was able to uproot boulders and heave them at this car! I guess he and Wright will both get life, eh?"