Then, as if to show that man was puny, a sudden wind howled from the north-west. The wind erupted so abruptly that Sharpe half twisted in the saddle, fearing an exploding shell behind him, and as he turned there was a booming discharge of thunder that sounded like the end of time itself. The rift in the clouds closed as though a vast door had slammed in heaven, and the reverberation of the door was the horrendous thunder that hammered down at the earth in a deafening cascade. A spear of lightning sliced blue-white into the far woods, and then the rain came.

In an instant the whole battlefield was blotted from sight. It was a cloudburst, a torrent, a seething pelting storm that slashed down to soak the fields and flood the ditches and hiss where it hit the hot barrels of the cannons. Sharpe had to shout to make himself heard over the downpour. “Let’s go! Come on!”

Within seconds the field had been churned into a morass. The rain was even heavier than the great sky-shaking storms Sharpe had seen in India. As he led his companions out from the trees’ shelter he had to duck his head against the maniacal force of the wind-whipped torrents that soaked his uniform in seconds. The horses struggled against the gale of rain, their hooves sticking in the glutinous mess of mud and straw. The rainwater sluiced off the fields with its load of precious soil, uncovering the white swollen bodies of the barely buried dead.

Thunder cracked in the sky; a battle of Gods that drowned the man-made sounds of war. The vast explosions rumbled from west to east, rebounded, split the clouds with multiple forks of lightning, and deluged the crouching earth. Sharpe led Harper and Doggett onto the Nivelles road that was now a writhing river of water-carried mud. He could see a troop of cloaked cavalry to his left, and a gun team hitching their weapon to its limber on his right, but any object more than thirty yards away was utterly obscured by the silver shafts of rain that crashed down like shrapnel. Behind Sharpe a gun fired, its sound drowned by the greater violence of the storm.

Sharpe turned onto the main highway. The paved surface was firmer; a causeway out of disaster. The hooves of those cavalry horses who struggled northwards in the flanking fields were clubbed with earth; proof that no gun would escape unless it reached the road.

“Move! Move! Move!” Gunners whipped their horses up from the fields onto the road that was swimming with a chalky white effluent. The horses strained, seemingly sensing their masters‘ panic caused by the near presence of enemy lancers. Men glanced behind into the storm-blotted landscape, then whipped at the gun teams till at last the horse artillery was clear of Quatre Bras and galloping northwards with blood dripping from the horses’ whipped flanks and water spraying silver off the gun wheels. Sharpe, Harper and Doggett raced with them.

Miraculously no gun was lost. The mad charge was checked at the village of Genappe where the road narrowed as it twisted between the thatched cottages. The delay gave the French pursuit a chance to catch the rearmost guns, but a regiment of British Dragoons turned and charged the Lancers. More French cavalry spurred forward and it took an assault by the heavy Life Guards, the sovereign’s own escort, to drive the Frenchmen away. The Life Guards, scarlet coated and wearing black and gold Grecian cockscomb helmets, hammered at the enemy with their ungainly heavy swords. The sheer weight of the heavy cavalry drove the lighter French horsemen back, giving the guns time to thread the narrow village street.

North of Genappe the French pursuit seemed to lose its ferocity. The rain also slackened, though it was still heavy. Every mile or so the British guns would stop, unlimber, fire a few rounds at their pursuers, then gallop on. The French were never far behind, but did not press home. The British cavalry, Dragoons and Life Guards, hovered on the flanks. Every few moments, when a French squadron trotted close, the British would advance, but each time the French declined to fight. Sharpe was amused to see that if a Life Guardsman tumbled from a slipping horse the man would remount, then hide his soiled uniform in the rear rank of his troop, just as if he was on parade in Hyde Park.

The French managed to bring up some of their own light eight-pounder cannons that opened fire with roundshot. The small cannon-balls fountained a slurry of mud and water wherever they landed. The mud was saving the retreat, not only soaking up the power of the French roundshot, but forcing the French cavalry to stay close to the high road. If the land had been dry the quick light enemy horse could have raced far round the British flanks to come slashing in with lance and sabre on the struggling column, but the mud and rain held them back.

Another weapon came to the British aid. A sudden crashing hiss made Sharpe twist round to see a rocket being fired. He had fought with rockets in Spain, but familiarity did not blunt his fascination with the odd weapon and he watched enthralled as the ungainly missile hurled itself forward on its pillar of flame that scorched the long stick that gave the rocket its balance. Doggett, who had never seen the new and mysterious weapon, was impressed, but Harper shook his head scornfully. “They’re guaranteed to miss every time, Mr Doggett. You just watch.”

The first rocket arched in fire across the damp valley to leave a serpentine trail of smoke. The missile fell towards the French guns, then the fuse inside its head exploded and a rain of red-hot shrapnel crashed down to slaughter every man in a French gun crew.

“Good God Almighty,” Harper said in astonished wonder, “the bloody thing worked!”

Encouraged by their success, the rocket artillery fired a whole barrage. Twelve rockets were fired from twelve metal troughs angled upwards on short legs. The rockets’ fuses were lit, then the rocketmen ran for cover. The missiles began to spew flames and smoke. For a few seconds they quivered in their firing troughs, then one by one they shot up into the wet air. They wobbled at first, then their acceleration hurled them on. Two streaked straight up into the clouds and disappeared, three dived into the wet meadow where their rocket flames seared the wet grass as the missiles circled crazily, five went vaguely towards the French but dived to earth long before they did any damage, and two circled back towards the British cavalry who stared for a second, then scattered in panic.

“That’s more like it,” Harper said happily. “That’s how they always used to be, isn’t that so, Mr Sharpe?”

But Sharpe was neither listening, nor watching the barrage. Instead he was staring across the highway to where a group of horsemen had scattered frantically away from the rogue rocket’s threat. Lord John Rossendale had been among the small group, but, in his effort to find safety, was now separated from his friends.

“I’ll join you up the road,” Sharpe said to Harper.

“Sir?” Harper was startled, but Sharpe had already twisted his horse away. And gone.

Lord John Rossendale could not remember being so wet, elated, frightened, or confused. Nothing made sense to him. He expected a battle — and the retreat seemed like a battle to him — to be something orderly and well managed. Officers should give loud confident orders which the men would smartly obey and to which the enemy would dutifully yield, but instead he was surrounded by disorder. Strangely the actors in that disorder seemed to understand what needed to be done. He watched a battery of horse artillery unlimber and go into action. No orders were given that Rossendale could hear, but the men knew exactly what to do, did it with cheerful efficiency, then limbered up to continue their mad careering gallop through the rain. Once, standing his horse in the pelting flood, Lord John had been shocked to hear a voice yelling at him to bloody well move his arse and Lord John had skipped his horse smartly aside only to see that it was a mere sergeant who had shouted. A second later a gun slewed in a spray of mud to occupy the very place where Lord John’s horse had been standing. Ten seconds later the gun fired, appalling Lord John with its sound and the violence of its recoil. In Hyde Park, which was the only place Lord John had ever seen cannons fired before, the polished guns made a decorous bang and, because there was no missile packed down onto the charge, such guns hardly moved at all, but this weapon, dirty, muddy and blackened, seemed to explode in noise and flame. Its wheels lifted clear out of the mud as its trail was driven back like a plough before the tons of metal and wood crashed down and its mud-covered crew ran forward to serve the smoking beast with sponges and rammers.