It was this last factor which provided its own solution to the problem of re-settling the migrant populations of the new Earth. The steady decline in mammalian fertility, and the growing ascendancy of amphibian and reptile forms best adapted to an aquatic life in the lagoons and swamps, inverted the ecological balances, and by the time of Kerans' birth at Camp Byrd, a city of ten thousand in Northern Greenland, it was estimated that fewer than five million people were still living on the polar caps.

The birth of a child had become a comparative rarity, and only one marriage in ten yielded any offspring. As Kerans sometimes reminded himself, the genealogical tree of mankind was systematically pruning itself, apparently moving backwards in time, and a point might ultimately be reached where a second Adam and Eve found themselves alone in a new Eden.

Riggs noticed him smiling to himself at this conceit. "What's amusing you, Robert? Another of your obscure jokes? Don't try to explain it to me."

"I was just casting myself in a new role." Kerans looked out over the ramp at the office blocks sliding past twenty feet away, the wash from the cutter splashing through the open windows along the water-line. The sharp tang of wet lime contrasted freshly with the over-sweet odours of the vegetation. Macready had taken them into the shadow of the buildings and it was pleasantly cool behind the breaking spray.

Across the lagoon he could see the portly bare-chested figure of Dr. Bodkin on the starboard bridge of the testing station, the Paisley cummerbund around his waist and the green celluloid shade shielding his eyes making him look like a riverboat gambler on his morning off. He was plucking the orange-sized berries from the ferns overhanging the station and tossing them up at the chittering marmosets dangling from the branches above his head, egging them on with playful shouts and whistles. Fifty feet away, on a projecting cornice, a trio of iguanas watched with stony disapproval, whipping their tails slowly from side to side in a gesture of impatience.

Macready swung the tiller, and they pivoted in a fan of spray into the lee of a tall white-faced building which lifted a full twenty storeys out of the water. The roof of an adjacent smaller block served as a jetty, next to which was moored a rusty white-hulled power cruiser. The raked perspex windows of the driving cabin were cracked and stained, and the exhaust vents leaked a scaly oil onto the water.

As the cutter jockeyed in behind the power cruiser under Macready's expert hand, they clambered over to the wire door, jumped down onto the jetty and crossed a narrow metal gangway that led into the apartment block. The walls of the corridor were slick with moisture, huge patches of mould feeding on the plaster, but the elevator was still working, powered by an emergency diesel. They rose slowly towards the roof, and stepped out on to the upper level of the duplex, then walked down a service corridor to the outer deck.

Directly below them was the lower level, a small swimming pooi with a covered patio, bright deck chairs drawn up in the shade by the diving board. Yellow venetian blinds masked the windows around three sides of the pool, but through the vanes they could see the cool shadows in the interior lounge, the glint of cut-glass and silver on the occasional tables. In the dim light under the striped blue awning at the rear of the patio was a long chromium counter, as inviting as an air-conditioned bar seen from a dusty street, glasses and decanters reflected in a diamond-paned mirror. Everything in this private haven seemed clean and discreet, thousands of miles away from the fly-blown vegetation and tepid jungle water twenty storeys below.

Beyond the far end of the pool, screened by an ornamental balcony, was a wide open view of the lagoon, the city emerging from the encroaching jungle, flat sheets of silver water expanding towards the green blur along the southern horizon. Massive silt banks lifted their backs through the surface, a light yellow fur along their spines marking the emergence of the first giant bamboo groves.

The helicopter rose from its platform on the roof of the base and arced upwards into the air towards them, the pilot swinging the tail as he changed direction, then roared overhead, two men in the open hatchway searching the rooftops with binoculars.

Beatrice Dahl lay back on one of the deck chairs, her long oiled body gleaming in the shadows like a sleeping python. The pink-tipped fingers of one hand rested lightly on an ice-filled glass on a table beside her, while the other hand turned slowly through the pages of a magazine. Wide blue-black sunglasses hid her smooth sleek face, but Kerans noted the slightly sullen pout of her firm lower lip. Presumably Riggs had annoyed her, forcing her to accept the logic of his argument.

The Colonel paused at the rail, looking down at the beautiful supple body with ungrudging approval. Noticing him, Beatrice pulled off her sunglasses, then tightened the loose back-straps of her bikini under her arms. Her eyes glinted quietly.

"All right, you two, get on with it. I'm not a strip show."

Riggs chuckled and trotted down the white metal stairway, Kerans at his heels, wondering how he was going to persuade Beatrice to leave her private sanctuary.

"My dear Miss Dahl, you should be flattered that I keep coming to see you," Riggs told her, lifting back the awning and sitting down on one of the chairs. "Besides, as the military governor of this area-" here he winked playfully at Kerans "-I have certain responsibilities towards you. And vice versa."

Beatrice regarded him briefly with a jaundiced eye and reached out to turn up the volume of the radiogram behind her. "Oh God…" She muttered some further, less polite imprecation under her breath and looked up at Kerans. "And what about you, Robert? What brings you out so early in the day?"

Kerans shrugged, smiling at her amiably. "I missed you."

"Good boy. I thought perhaps that the gauleiter here had been trying to frighten you with his horror stories."

"Well, he has, as a matter of fact." Kerans took the magazine propped against Beatrice's knee and leafed through it idly. It was a forty-year-old issue of Paris Vogue, from its icy pages evidently kept somewhere in cold storage. He dropped it on the green-tiled floor. "Bea, it looks as if we'll all have to leave here in a couple of days' time. The Colonel and his men are pulling out for good. We can't very well stay on after he's gone."

"_We?_" she repeated dryly. "I didn't know there was any chance of your staying behind?"

Kerans glanced involuntarily at Riggs, who was watching him steadily. "There isn't," he said firmly. "You know what I mean. There'll be a lot to do in the next forty-eight hours, try not to complicate things by making a last emotional stand."

Before the girl could cut back at Kerans, Riggs added smoothly: "The temperature is still going up, Miss Dahl, you won't find it easy to stand one hundred and thirty degrees when the fuel for your generator runs out. The big Equatorial rain belts are moving northward, and they'll be here in a couple of months. When they leave, and the cloud cover goes, the water in that pool-" he indicated the tank of steaming, insect-strewn fluid "-will damn nearly boil. What with the Type X Anopheles, skin cancers and the iguanas shrieking all night down below, you'll get precious little sleep." Closing his eyes, he added pensively: "That is, assuming that you still want any."

At this last remark the girl's mouth fretted slightly. Kerans realised that the quiet ambiguity in Riggs' voice when he asked how the biologist slept had not been directed at his relationship with Beatrice.

The Colonel went on: "In addition, some of the human scavengers driven northward out of the Mediterranean lagoons won't be too easy to deal with."

Beatrice tossed her long black hair over one shoulder. "I'll keep the door locked, Colonel."

Irritated, Kerans snapped: "For God's sake, Beatrice, what are you trying to prove? These self-destructive impulses may be amusing to play with now, but when we've gone they won't be so funny. The Colonel's only trying to help you-he doesn't really give a hoot whether you stay behind or not."

Riggs let out a brief laugh. 'Well, I wouldn't say that. But if the thought of my personal concern worries you so much, Miss Dahl, you can just put it down to my over-developed sense of duty."

"That's interesting, Colonel," Beatrice commented sarcastically. "I've always understood that our duty was to stay on here as long as possible and make every sacrifice necessary to that end. Or at least-" here the familiar gleam of sharp humour crossed her eyes "-that was the reason my grandfather was given when the government confiscated most of his property." She noticed Riggs peering over his shoulder at the bar. "What's the matter, Colonel? Looking for your punkahwallah? I'm not going to get you a drink, if that's what you're after. I think you men only come up here to booze."

Riggs stood up. "All right, Miss Dahl. I give in. I'll see you later, Doctor." He saluted Beatrice with a smile. "Some time tomorrow I'll send the cutter over to collect your gear, Miss Dahl."

When Riggs had gone Kerans lay back in his chair, watching the helicopter circle over the adjacent lagoon. Now and then it dived along the water's edge, the down-draught from its rotor blades beating through the flapping fronds of the fern trees, driving the iguanas across the rooftops. Beatrice brought a drink from the bar and sat down on the chair at his feet.

"I wish you wouldn't analyse me in front of that man, Robert." She handed him the drink and then leaned against his knees, resting her chin on one wrist. Usually she looked sleek and well-fed, but her expression today seemed tired and wistful.

"I'm sorry," Kerans apologised. "Perhaps I was really analysing myself. Riggs' ultimatum came as a bit of a surprise; I wasn't expecting to leave so soon."

"You are going to leave then?"

Kerans paused. The automatic player in the radiogram switched from Beethoven's Pastoral to the Seventh, Toscanini giving way to Bruno Walter. All day, without a break, it played through the cycle of nine symphonies. He searched for an answer, the change of mood, to the sombre opening motif of the Seventh, overlaying his indecision.

"I suppose I want to, but I haven't yet found an adequate reason. Satisfying one's emotional needs isn't enough. There's got to be a more valid motive. Perhaps these sunken lagoons simply remind me. of the drowned world of my uterine childhood-if so, the best thing is to leave straight away. Everything Riggs says is true. There's little hope of standing up to the rainstorms and the malaria."