Berthing the catamaran against the landing stage, Kerans shipped the outboard and then made his way up the gangway into the base. As he let himself through the screen hatch he looked back over his shoulder across the lagoon, and caught a brief glimpse through the heat waves of Beatrice standing at her balcony rail. When he waved, however, she characteristically turned away without responding.

"One of her moody days, Doctor?" Sergeant Macready stepped from the guard cubicle, a trace of humour relaxing his beak-like face. "She's a strange one, all right."

Kerans shrugged. "These tough bachelor girls, you know, Sergeant. If you're not careful they frighten the wits out of you. I've been trying to persuade her to pack up and come with us. With a little luck I think she will."

Macready peered shrewdly at the distant roof of the apartment house. "I'm glad to hear you say so, Doctor," he ventured noncommittally, but Kerans was unable to decide if his scepticism was directed at Beatrice or himself.

Whether or not they finally stayed behind, Kerans had resolved to maintain the pretence that they were leaving-every spare minute of the next three days would be needed to consolidate their supplies and steal whatever extra equipment they required from the base stores. Kerans had still not made up his mind-once away from Beatrice his indecision returned (ruefully he wondered if she was deliberately trying to confuse him, Pandora with her killing mouth and witch's box of desires and frustrations, unpredictably opening and shutting the lid)-but rather than stumble about in a state of tortured uncertainty, which Riggs and Bodkin would soon diagnose, he decided to postpone a final reckoning until the last moment possible. Much as he loathed the base, he knew that the sight of it actually sailing off would act as a wonderful catalyst for emotions of fear and panic, and any more abstract motives for staying behind would soon be abandoned. A year earlier, he had been accidentally marooned on a small key while taking an unscheduled geomagnetic reading, the departure siren muffled by his headphones as he crouched over his instruments in an old basement bunker. When he emerged ten minutes later and found the base six hundred yards away across a widening interval of flat water he had felt like a child parted forever from its mother, barely managed to control his panic in time to fire a warning shell from his flare pistol.

"Dr. Bodkin asked me to call you as soon as you arrived, sir. Lieutenant Hardman hasn't been too happy this morning."

Kerans nodded, glancing up and down the empty deck. He had taken lunch with Beatrice, knowing that the base was deserted in the afternoons. Half the crew were away with either Riggs or the helicopter, the rest asleep in their bunks, and he had hoped to carry out a private tour of the stores and armoury. Now unluckily, Macready, the Colonel's ever-alert watch-dog, was hanging about at his heels, ready to escort him up the companionway to the sick-bay on B-Deck.

Kerans studiously examined a pair of Anopheles mosquitos which bad slipped through the wire hatch behind him. "They're still getting in," he pointed out to Macready. 'What's happened to the double screening you were supposed to be putting up?"

Swatting at the mosquitos with his forage cap, Macready looked around uncertainly. A secondary layer of screening around the wire mesh enclosing the base had long been one of Colonel Riggs' pet projects. At times he would tell Macready to detail a squad to carry out the work, but as this involved sitting on a wooden trestle in the open sunlight in the centre of a cloud of mosquitos only a few token sections around Riggs' cabin had been completed. Now that they were moving northward the utility of the project had. faded, but Macready's Presbyterian conscience, once roused, refused to let him rest.

"I'll get the men on to it this evening, Doctor," he assured Kerans, pulling a ball-pen and note-book from his hip pocket.

"No hurry, Sergeant, but if you've nothing better to do, I know the Colonel's very keen." Kerans left him squinting along the metal louvres and walked off along the deck. As soon as he was out of sight he stepped through the first doorway.

C-Deck, the lowest of the three decks comprising the base, contained the crew's quarters and galley. Two or three men lay about among their tropical gear in the cabins, but the recreation room was empty, a radio playing to itself by the table-tennis tournament board in the corner. Kerans paused, listening to the strident rhythms of the guitar music, overlayed by the distant blare of the helicopter circling over the next lagoon, then made his way down the central stair-well which led to the armoury and workshops housed in the pontoon.

Three-quarters of the hull was occupied by the 2,000 hp. diesels which powered the twin screws, and by the oil and aviation fuel tanks, and the workshops had been temporarily transferred during the final aerial sweeps to two vacant offices on A-Deck, beside the officers' quarters, so that the mechanics could service the helicopter with the maximum speed.

The armoury was closed when Kerans entered, a single light burning in the tech, corporal's glass-walled booth. Kerans gazed around the heavy wooden benches and cabinets lined with carbines and submachine-guns. Steel rods through the trigger guards locked the weapons into their cases, and he idly touched the heavy stocks, doubting whether he could handle any of the weapons even if he stole one. In a drawer at the testing station was a Colt.45 and fifty rounds issued to him three years earlier. Once a year he made an official return on the ammunition discharged-in his case none-and exchanged the unused shells for a fresh issue, but he had never tried to fire the pistol.

On his way out he scanned the dark green ammunition boxes stacked around the wall below the cabinets, all of them doublepadlocked. He was passing the booth when the light through the door illuminated the dusty labels on a row of metal cartons below one of the work benches.

'Hy-Dyne.' On an impulse Kerans stopped, pushed his fingers through the wire cage and brushed the dust off a label, tracing the formula with his fingers. 'Cyclotrime-thylenetrinitramine: Gas discharge speed-8,000 metres/second.'

Speculating on the possible uses of the explosive-it would be a brilliant tour de force to sink one of the office buildings into the exit creek after Riggs had left, blocking any attempt to return-he leaned his elbows on the bench, playing absent-mindedily with a 4-inch-diameter brass compass that had been left for repair. The calibrated annulus was loose and had been rotated a full 180 degrees, the point emphasised with a chalked cross.

Still thinking about the explosive, and the possibility of stealing detonators and fuse-wire, Kerans rubbed away the blunt chalk marks and then lifted the compass and weighed it in his hand. Leaving the armoury, he began to climb the stairway, uncaging the compass and letting the pointer dance and float. A sailor walked past along C-Deck, and Kerans quickly slipped the compass into his jacket pocket.

Suddenly, as he visualised himself throwing his weight onto the handles of a plunger box and catapulting Riggs, the base and the testing station into the next lagoon, he stopped and steadied himself against the rail. Smiling ruefully at the absurdity of the fantasy, he wondered why he had indulged it.

Then he noticed the heavy cylinder of the compass dragging at his jacket. For a moment he peered down at it thoughtfully.

"Watch out, Kerans," he murmured to himself. "You're living on two levels."

Five minutes later, when he entered the sick-bay on B-Deck, he found more urgent problems facing him.

Three men were being treated for heat ulcers in the dispensary, but the main twelve-bed ward was empty. Kerans nodded to the corporal issuing penicillin band-aids and walked through to the small single ward on the starboard side of the deck.

The door was closed, but as he turned the handle he could hear the restless heaving motion of the cot, followed by a fractious muttering from the patient and Dr. Bodkin's equable but firm reply. For a few moments the latter continued to speak in a iow even monologue, punctuated by a few shrugging protests and concluded by an interval of tired silence.

Lieutenant Hardman, the senior pilot of the helicopter (now being flown by his co-pilot, Sergeant Daley) was the oniy other commissioned member of the survey unit, and until the last three months had served as Riggs' deputy and chief executive officer. A burly, intelligent but somewhat phlegmatic man of about 30, he had quietly kept himself apart from the other members of the unit. something of an amateur naturalist, he made his own descriptive notes of the changing flora and fauna, employing a taxonomic system of his own devising. In one of his few unguarded moments he had shown the notebooks to Kerans, then abruptly withdrawn into himself when Kerans tactfully pointed out that the classifications were confused.

For the first two years Hardman had been the perfect buffer between Riggs and Kerans. The rest of the crew took their cue from the Lieutenant, and this had the advantage, from Kerans' point of view, that the group never developed that sense of happy cohesion a more extravert second-in-command might have instilled, and which would have soon made life unbearable. The loose fragmentary relationships aboard the base, where a replacement was accepted as a fully paid up member of the crew within five minutes and no-one cared whether he had been there two days or two years, was largely a reflection of Hardman's temperament. When he organised a basketball match or a regatta out on the lagoon there was no self-conscious boisterousness, but a laconic indifference to whether anyone took part or not.

Recently, however, the more sombre elements in Hardman's personality had begun to predominate. Two months earlier he complained to Kerans of intermittent insomnia-often, from Beatrice Dahl's apartment, Kerans would watch him long after midnight standing in the moonlight beside the helicopter on the roof of the base, looking out across the silent lagoon-and then took advantage of an attack of malaria to excuse himself from flying duty. Confined to his cabin for up to a week on end, he steadily retreated into his private world, going through his old note-books and running his fingers, like a blind man reading Braille, across the glass display cases with their few mounted butterflies and giant moths.

The malaise had not been difficult to diagnose. Kerans recognised the same symptoms he had seen in himself, an accelerated entry Into his own 'zone of transit', and left the Lieutenant alone, asking Bodkin to call in periodically.