“Are they defeated?” asked Strange.

“No, but they have retreated and so the Duke says we must do the same. His Grace has chosen somewhere to fight and the Prussians will meet us there. A place called Waterloo.”

“Waterloo? What a ridiculously odd name!” said Strange.

“It is odd, is it not? I could not find it on the map.”

“Oh!” said Strange. “This was continually happening in Spain! No doubt the fellow who told you got the name wrong. Depend upon it, there is no such place as Waterloo!”

A little after noon they mounted their horses and were about to follow the Army out of the village, when a message arrived from Wellington: a squadron of French lancers was approaching and could Mr Strange do something to annoy them? Strange, anxious to avoid another accusation of Vauxhall-Gardens magic, asked Hadley-Bright’s advice. “What do cavalry hate the most?”

Hadley-Bright thought for a moment. “Mud,” he said.

“Mud? Really? Yes, I suppose you are right. Well, there are few things more plain and workman-like than weather magic!”

The skies darkened. An inky thundercloud appeared; it was as large as all Belgium and so full and heavy that its ragged skirts seemed to brush the tops of the trees. There was a flash and the world turned bone-white for an instant. There was a deafening crack and the next moment the rain came down in such torrents that the earth boiled and hissed.

Within minutes the surrounding fields had turned to a quagmire. The French lancers were quite unable to indulge in their favourite sport of fast and dextrous riding; Wellington’s rearguard got safely away.

An hour later Strange and Hadley-Bright were surprized to discover that there was indeed a place called Waterloo and that they had arrived at it. The Duke was sitting on his horse in the rain, gazing in high good humour at the filthy men, horses and carts. “Excellent mud, Merlin!” he called out cheerfully. “Very sticky and slippery. The French will not like it at all. More rain, if you please! Now, you see that tree where the road dips down?”

“The elm, your Grace?”

“The very one. If you will stand there during the battle tomorrow, I will be much obliged to you. I will be there some of the time, but probably not very often. My boys will bring you your instructions.”

That evening the various divisions of the Allied Army took up positions along a shallow ridge south of Waterloo. Above them the thunder roared and the rain came down in torrents. From time to time deputations of bedraggled men approached the elm-tree and begged Strange to make it stop, but he only shook his head and said, “When the Duke tells me to stop, I shall.”

But the veterans of the Peninsular War remarked approvingly that rain was always an Englishman’s friend in times of war. They told their comrades: “There is nothing so comforting or familiar to us, you see – whereas other nations it baffles. It rained on the nights before Fuentes, Salamanca and Vitoria.” (These were the names of some of Wellington’s great victories in the Peninsula.)