‘Somebody was in a hurry,’ I said aloud. I depressed the lid and polished the initials with my fingertips. ‘This must have belonged to one of the members of the survey. C. F. N. Do you want to send it on to him?’

Tallis watched me pensively. ‘No. I’m afraid the two members of the team died here. Just over a year ago.’

He told me about the incident. Two Cambridge geologists had negotiated through the Institute for Tallis’s help in establishing a camp ten miles out in the volcano jungle, where they intended to work for a year, analysing the planet’s core materials. The cost of bringing a vehicle to Murak was prohibitive, so Tallis had transported all the equipment to the camp site and set it up for them.

‘I arranged to visit them once a month with power packs, water and supplies. The first time everything seemed all right. They were both over sixty, but standing up well to the heat. The camp and laboratory were running smoothly, and they had a small transmitter they could have used in an emergency.

‘I saw them three times altogether. On my fourth visit they had vanished. I estimated that they’d been missing for about a week. Nothing was wrong. The transmitter was working, and there was plenty of water and power. I assumed they’d gone out collecting samples, lost themselves and died quickly in the first noon high.’

‘You never found the bodies?’

‘No. I searched for them, but in the volcano jungle the contours of the valley floors shift from hour to hour. I notified the Institute and two months later an inspector flew in from Ceres and drove out to the site with me. He certified the deaths, told me to dismantle the camp and store it here. There were a few personal things, but I’ve heard nothing from any friends or relatives.’

‘Tragic,’ I commented. I closed the tape recorder and carried it into the shed. We walked back to the cabin. It was an hour to noon, and the parabolic sun bumper over the roof was a bowl of liquid fire.

I said to Tallis: ‘What on earth were they hoping to catch in the volcano jungle? The sonic trip was set.’

‘Was it?’ Tallis shrugged. ‘What are you suggesting?’

‘Nothing. It’s just curious. I’m surprised there wasn’t more of an investigation.’

‘Why? To start with, the fare from Ceres is £800, over £3000 from Earth. They were working privately. Why should anyone waste time and money doubting the obvious?’

I wanted to press Tallis for detail, but his last remark seemed to close the episode. We ate a silent lunch, then went out on a tour of the solar farms, replacing burnt-out thermo-couples. I was left with a vanished tape, two deaths, and a silent teasing suspicion that linked them neatly together.

Over the next days I began to watch Tallis more closely, waiting for another clue to the enigma growing around him.

I did learn one thing that astonished me.

I had asked him about his plans for the future; these were indefinite — he said something vague about a holiday, nothing he anticipated with any eagerness, and sounded as if he had given no thought whatever to his retirement. Over the last few days, as his departure time drew closer, the entire focus of his mind became fixed upon the volcano jungle; from dawn until late into the night he sat quietly in his chair, staring out at the ghostless panorama of disintegrating cones, adrift in some private time sea.

‘When are you coming back?’ I asked with an attempt at playfulness, curious why he was leaving Murak at all.

He took the question seriously. ‘I’m afraid I won’t be. Fifteen years is long enough, just about the limit of time one can spend continuously in a single place. After that one gets institutionalized—’

‘Continuously?’ I broke in. ‘You’ve had your leaves?’

‘No, I didn’t bother. I was busy here.’

‘Fifteen years!’ I shouted. ‘Good God, why? In this of all places! And what do you mean, "busy"? You’re just sitting here, waiting for nothing. What are you supposed to be watching for, anyway?’

Tallis smiled evasively, started to say something and then thought better of it.

The question pressed round him. What was he waiting for? Were the geologists still alive? Was he expecting them to return, or make some signal? As I watched him pace about the cabin on his last morning I was convinced there was something he couldn’t quite bring himself to tell me. Almost melodramatically he watched out over the desert, delaying his departure until the thirty-minute take-off siren hooted from the port. As we climbed into the half-track I fully expected the glowing spectres of the two geologists to come looming out of the volcano jungle, uttering cries of murder and revenge.

He shook my hand carefully before he went aboard. ‘You’ve got my address all right? You’re quite sure?’ For some reason, which confused my cruder suspicions, he had made a special point of ensuring that both I and the Institute would be able to contact him.

‘Don’t worry,’ I said. ‘I’ll let you know if it rains.’

He looked at me sombrely. ‘Don’t wait too long.’ His eyes strayed past my head towards the southern horizon, through the sand-haze to the endless sea of cones. He added: ‘Two million years is a long time.’

I took his arm as we walked to the ramp. ‘Tallis,’ I asked quietly, ‘what are you watching for? There’s something, isn’t there?’

He pulled away from me, collected himself. ‘What?’ he said shortly, looking at his wristwatch.

‘You’ve been trying to tell me all week,’ I insisted. ‘Come on, man.’

He shook his head abruptly, muttered something about the heat and stepped quickly through the lock.

I started to shout after him: ‘Those two geologists are out there… but the five-minute siren shattered the air and by the time it stopped Tallis had disappeared down the companionway and crewmen were shackling on the launching gantry and sealing the cargo and passenger locks.

I stood at the edge of the port as the ship cleared its take-off check, annoyed with myself for waiting until the last impossible moment to press Tallis for an explanation. Half an hour later he was gone.

Over the next few days Tallis began to slide slowly into the back of my mind. I gradually settled into the observatory, picked out new routines to keep time continuously on the move. Mayer, the metallurgist down at the mine, came over to the cabin most evenings to play chess and forget his pitifully low extraction rates. He was a big, muscular fellow of thirty-five who loathed Murak’s climate, geology and bad company, a little crude but the sort of tonic I needed after an overdose of Tallis.

Mayer had met Tallis only once, and had never heard about the deaths of the two geologists.

‘Damned fools, what were they looking for? Nothing to do with geology, Murak hasn’t got one.’

Pickford, the old agent down at the depot, was the only person on Murak who remembered the two men, but time had garbled his memories.

‘Salesmen, they were,’ he told me, blowing into his pipe. ‘Tallis did the heavy work for them. Should never have come here, trying to sell all those books.’

‘Books?’

‘Cases full. Bibles, if I recall.’

‘Textbooks,’ I suggested. ‘Did you see them?’

‘Sure I did,’ he said, puttering to himself. ‘Guinea moroccos.’ He jerked his head sharply. ‘You won’t sell them here, I told them.’

It sounded exactly like a dry piece of academic humour. I could see Tallis and the two scientists pulling Pickford’s leg, passing off their reference library as a set of commercial samples.

I suppose the whole episode would eventually have faded, but Tallis’s charts kept my interest going. There were about twenty of them, half million aerials of the volcano jungle within a fifteen-mile radius of the observatory. One of them was marked with what I assumed to be the camp site of the geologists and alternative routes to and from the observatory. The camp was just over ten miles away, across terrain that was rough but not over-difficult for a tracked car.