The first sign, in the sky, of the coming change was a ragged tuft of greasy warm cloud. Brown, streaked with red and yellow tints, it had hovered above the ocean for two days, rising in temperature and gathering an ever more powerful charge of negative ions. It must have been about three o’clock in the afternoon of the third day that this stained, suspended rag – like the cloth of a cook or a mechanic – began to roll about itself. Cold air rushed into its warmth from all sides, creating a partial vacuum and a magnetic commotion of oppositely charged particles.

Birds were already flying inland – not to Zanzibar, for this presage of bad weather was as yet far away, but to Mombasa and Malindi. Long ago, they had felt a disturbance in the atmospheric equilibrium, sensing the change of monsoon that would occasion cyclones and hurricanes.

Winds began to eddy round the lone cloud, drawing others to it, swirling pouches of aqueous vapour. Elastic and compressible, each one brought a new colour to the original oily roll. Its reds and yellows multiplied in shade, black and purple were added, layer upon layer, streak upon streak – till the whole, driving across towards the mainland, presented that ugly and threatening appearance which enabled the rainmaker to bring the monsoon he in fact foresaw.

The elders of the Kenyan coast were wrong, this time, to say ‘the rains are coming’. The accumulating storm, diverted by the island of Lamu, was sucked back out to sea. Gyrating, gathering in size all the while, it moved horizontally across the waves, travelling northwards, now dark red, the burnt umber of the painter’s palette, now grey, with the appearance of a ball of smoke.

As it travelled northwards, along the Tanzanian coast, the cyclone increased its velocity and collected ever more violent winds about its centre. Smaller whirlings knitted to the initial motion; became larger themselves; gathered further gyrations in their turn.

So in a continuous, circling, progressive action, this remarkable mass of cloud and vapour, about forty-five miles in diameter, made its way towards Zanzibar. Of the power and nature which, according to the law of storms in western lands, is called a hurricane squall, this weather pattern is known, by the fishermen of the Swahili coast, as the chamchela. They would also know that the cyclone’s northward movement was unusual – tropical storms tend to move southerly – and therefore all the more worrying.

At the cyclone’s heart, even now as it impinged on an exposed bluff off Macpherson Cove and, forced to one side, was bounced once more out to sea, raindrops began to gather. They mixed with a fine mist of saltwater, spoondrift as mariners once called it, which was caught up from the crests of waves as the cyclone progressed. Its direction was a small atoll beyond Macpherson, an islet where turtles have been known to lay their eggs.

Below the chamchela, as it drove along, low over the water, the sea began to swell, rising heavily, sending eddies of increasing violence towards Lyly’s shore – where, as if to taste the salt that was filling the air, a bulky figure emerged from the ruined cottage.

Some way off, Nick Karolides floated in the tugging water, tensing himself for every wave. He had been there for about three quarters of an hour, spying on the men. For his island was now peopled. There were seven: the three men from the motor cruiser – those whose faces he recognised, those who were armed – and four others who had come in two small dhows.

The wooden fishing boats were pulling hard at their anchors in the Lyly lagoon. As with the poachers’ boat, they had been narrow enough to get through the gap in the reef. These were less rough in construction than the other dhow, but their unplaned, grey timbers and tattered sails still made them look like the marine equivalent of shanty-town dwellings. The cruiser itself was beached, its dark green pennant fluttering in the rising wind. He watched the figure go back inside the cottage.

From his vantage point, down in some reeds near the rocky outcrop that led out to the entrance of the underwater cave, Nick could see most of the beach. It was uncomfortable, lying in that muddy spot with his mask just above the surface. His legs were numb and he was worried that the silty water would clog his breathing apparatus – but otherwise it was a good place from which to watch.

There were a large number of crates on the beach in front of the cottage. The men were packing canisters, about the size of catering tins, tins of beans or juice, into the crates.

Not all the Arabs were doing this. The figure emerged again from the house. Nick could see the outline of a sub-machine gun hanging from a strap round his neck. The man was staring out to sea. To Nick it seemed as if he were staring directly at him. This man, bulky and unshaven, appeared utterly alert. It was almost as if he knew he was being watched.

Nick suddenly realised that the temperature had dropped, and the sky had darkened considerably. The lagoon, too, had changed colour, its blue trailing into black. A sudden, heavy wave lifted up the dhows.

The clouds were a sombre tangle, spinning rapidly through the lowering sky. He knew the signs now, he had been in the tropical belt long enough. A storm was coming in. He’d better get back to the yacht. Slowly, silently, he eased himself out of the reeds. There were crests of foam on the waves. A strong wind was blowing, and the current was running hard. It began to rain just as he dived, the big grey drops plummeting into the water like lead shot.

Leggatt had anchored some way off on the other side of the island, so they couldn’t be spotted, but Nick had plenty of air in his tanks. He swam deep to avoid the swell and detection – swam over sea fans, groupers and blennies, a carousel of trevally and a lone turtle flipping its way to calmer reaches – swam over these, but was thinking all the while about the metal canisters and the men with guns. He was panicking a little, if truth be told.

He was also thinking about Miranda. She had been back on the mainland for two days before he and Leggatt had managed to return to Lyly. There had been one email in the interim, thanking him for ‘a lovely weekend’, but it was rather formal and cold, he thought, as if signalling that nothing would come of what had happened. He felt disappointed, let down, having been under the impression that something deep and passionate might have been in the works.

The keel of the Winston Churchill was dark in the water. He swam round to the other side, to the rope ladder. Breaking the surface, he realised that the wind was much stronger now. He banged on the hull three times with the heel of his knife, to alert Leggatt. Climbing out of the water, he became conscious of the weight of his tank. Sounding on the metal, rain was falling heavily now. The boat was rocking from side to side in the current.

His blond mane flying in the rising wind, the old man was at the top, gripping the gunwale with one brown hand and holding out another to Nick.

‘You better come below!’ Leggatt shouted, as Nick released his harness and lowered his tank to the deck.

The rain was lancing into Leggatt’s face. ‘I don’t much like the look of this. Barometer’s dropped like a stone. I’ve had to reduce canvas twice already.’

Inside the cabin, rubbing himself with a coarse towel, Nick began telling the Englishman what he’d seen.

‘They had guns. They were packing crates –’

But the old man, he realised, wasn’t really listening.

‘Tell me later. I’m going up. I think it’s a cyclone.’

Once he was dressed, Nick joined Leggatt in the wheelhouse. The storm was gathering rapidly, wind battering against the wheelhouse door. Large grey waves cruised the surface as if they were something other than water – something of another order entirely. Rain hurled down.

Leggatt gripped the wheel. ‘We’re going to have to sit it out. We can’t heave anchor now, not in this.’

There was a clap of thunder, like God stamping his foot. Another wave unfurled itself against the deck. Its crest swept over the timbers. Straining on its chain, the Winston Churchill creaked fearfully as it absorbed the blow. The two men tried to keep their balance in the shifting wheelhouse. There was a brief moment of stillness – except for the lamp, which swung from side to side. Nick looked at Leggatt. Grim-faced, he was struggling with the wheel, the lamp casting its shaken light on his worn face. Another wave came, and the boat shuddered. It was terrifying how quickly the storm had risen.

‘Is there anything I can do?’ asked Nick, looking out at the thick clouds of broken water that rushed towards them.

Leggatt grunted, chewing anxiously on the end of his pipe. There was another peal of thunder, long and syncopated this time, petering out like a drum roll. The two of them stared out of the wheelhouse window. A jagged dart of lightning spurted across the sky. Lyly’s palm trees and lighthouse were invisible now. Fog had descended on the island, and a torrent of slanting rain. A blow hit the yacht. The noise of the storm itself was suddenly interrupted by a tearing sound, quite different from the groans of the timbers.

‘Oh Christ!’ shouted Leggatt, reaching for his cap where it hung on a hook and clapping it on his head. ‘That’s something down. You take the wheel. I’ll tie it when I get back. I’m going to have to take in more sail. We’re still quite close-rigged, and if I don’t take it all in we’ll drag.’

Nick gripped the varnished wood of the wheel. In spite of the anchor, it was still fighting the current. The Churchill was tilting. He didn’t know how it should feel, but this felt wrong, like a dancer out of kilter. He heard Leggatt sliding about on the deck behind him. He stared out of the rain-lashed glass. Through the window of the tiny cubicle, over a teak board spread with stained charts, binoculars, a sextant and other instruments, he could see waves bounding towards him. He found himself thinking suddenly about the Arabs on the island – how were they coping with this? – when another crashing sound came. Then a faint cry.

Hurriedly tying the wheel with a length of rope, Nick ran outside into driven water, to find Leggatt lying on his side next to a bollard. A fallen spar lay nearby, together with a tangle of sail and rope. There was blood in his blond hair. Either he had hit the bollard or the spar had hit him. Nick rushed over and knelt beside him, but the old man was already sitting up.

‘Get back down. I’m all right. Get back down. Carried away the jib.’

Nick ignored him. Quickly taking off his shirt, he pressed it to the wound on Leggatt’s head. The yacht began to heel to starboard.

‘The wheel.’

The old man was silent then, his head lolling forward onto his chest. For a few seconds, the storm seemed to lull again. There was a breath of cold air, and then Leggatt’s numbed eyes were opening, widening, looking over Nick’s shoulder.

The old man lifted his hand. Nick looked himself. An enormous sea was racing towards them. It was as if a mountain were bearing down on them, only it was alive – animal, foam-flecked, intense. There was something mesmerising about it … but Nick knew he had to get Leggatt inside. Gathering his arms and legs, he dragged him over the slippery deck towards the wheelhouse.

As he did so, however, the Englishman seemed to come to his senses.

The approaching wave towered above them, a rising world of water.

‘Rope,’ gasped Leggatt. ‘Get us in the guide rope.’

The two of them slid over to the safety rope that ran along the gunwale. Leggatt, whose face was streaming with blood, pulled the rope over his chest, and Nick followed his example. Above them, the wave curled, then tore down from its crest. They were flung against the rope as the water struck. Nick felt the send of the wave bodily, as its momentum moved everything on board. They scudded on, following the big wave like a toy boat. And then, as they swept along, there was a screech of timber, followed by the sound of inrushing water.

Something had stove in. Slowly but certainly, the Winston Churchill started to tip over.

‘Wait!’ shouted Leggatt, as Nick tried to scramble clear. ‘Wait till she’s gone.’

If it hadn’t been so dangerous, and Leggatt not injured, it might have been comic – something out of Chaplin or Harold Lloyd, the way the two of them, becoming ever more pendulous, hung from the guide rope at the top of the capsizing sloop.

As the mast hit the water, Leggatt shouted in Nick’s ear. ‘We have to get to the dinghy … if it isn’t torn off!’

Nick looked towards the bow. The little boat was still there – tugging at its leash, storm-tossed and filled with rainwater – but still there. Like a pair of monkeys, dangling crazily in mid-air, feet scrabbling against the streaming deck, they inched along the rope. The Winston Churchill was done for. Nick knew this; he felt shocked by the turn of events: the awareness that, less than an hour ago, the yacht had been floating peacefully. In a few minutes, it would sink like a block of concrete. And – if they didn’t reach it in time – take the dinghy down with it.

They made it with seconds to spare. Nick hauled the smaller boat alongside and dropped down into it, twisting his ankle painfully. Leggatt followed, falling in a heap on top of him.

‘Cut the rope!’ Leggatt shouted hoarsely, fumbling in his pocket and handing over his penknife.

Nick – God knows what had happened to his own knife – did as he said. Suddenly they were free. But not out of danger. Such a small boat was hardly up to the exigencies of a tropical storm. Yet there was no time to waste in consideration of their chances. Leggatt had already begun undoing the buckles that held the oars. Once they were unshipped and installed in the rowlocks, Nick began to heave the dinghy away from the crippled sloop. It was exhausting work in such heavy water, and they had not gone twenty feet before the last of the Churchill settled lower into the sea. There was a brief pause. Then, with a drawn-out creak, it disappeared beneath the waves.

Nick expected Leggatt to say something, but he was silent. Perhaps he was faint from the blood he had lost. He must, anyway, the younger man reflected, be devastated to see his pride and joy go down like that. Like losing a child. But he seemed oddly unmoved.

The storm, at least, was showing signs of abating. Although the waves were still very large, and there remained a danger of them being swamped in the dinghy, the rain had ceased. The sky had begun to clear. If he twisted round, Nick could just make out the pinnacle of Lyly’s lighthouse. At least they had a landmark. That was something. In the circumstances, that really was something.

Still shaken by how quickly it had all happened, Nick rowed on a little further. The dinghy slid up the waves – and then pitched down again. It seemed pointless, they were making so little progress. The boat might as well have been a beetle in a bathtub. Leggatt still hadn’t said anything.

Nick himself spoke. ‘I’m sorry, Ralph.’

Wild and bloody, Leggatt looked up and laughed out loud.

‘I’m less worried about the boat than those fellows with guns.’ Then he laughed again, manically.

Had the knock on the head made him delirious? Unnerved by the mirthless laughter, Nick replied slowly. ‘Do you think we should head for the mainland instead?’

The Englishman grunted, and looked down into the bottom of the rowing boat, where dirty water was slopping to and fro. Then, as if the sight of it had brought home to him their true plight, he suddenly returned to his customary solidity.

‘In an eight-foot dinghy? We’d never make it. I think we should carry on for Lyly, lie off it out of sight till nightfall, then steal one of their dhows under cover of darkness. Or the cruiser?’

It sounded a far-fetched plan, but without saying anything, Nick began rowing again, arching his back against the pressure exerted on the wooden blades. The sea had fallen silent now. The only sound was the rattle of the oars and the quiet lap of water against the bow. The sky was like the inside of a red shell. Behind him, he knew, loomed the shape of the island. But in his imagination its familiar features were obscured by the silhouettes of men. Their figures moved across the blooded air. Their postures were determined. Also, as Leggatt said, they were armed.