It was ten days short of Candlemas, 1814, and an Atlantic wind carried shivers of cold rain that slapped on narrow cobbled alleys, spilt from the broken gutters of tangled roofs, and pitted the water of St Jean de Luz’s inner harbour. It was a winter wind, cruel as a bared sabre, that whirled chimney smoke into the low January clouds shrouding the corner of south-western France where the British Army had its small lodgement.

A British soldier, his horse tired and mud-stained, rode down a cobbled street in St Jean de Luz. He ducked his head beneath a baker’s wooden sign, edged his mare past a fish-cart, and dismounted at a corner where an iron bollard provided a tethering post for the horse. He patted the horse, then slung its saddle-bags over his shoulder. It was evident he had ridden a long way.

He walked into a narrow alley, searching for a house that he only knew by description; a house with a blue door and a line of cracked green tiles above the lintel. He shivered. At his left hip there hung a long, metal-scabbarded sword, and on his right shoulder was a rifle. He stepped aside for a woman, black-dressed and squat, who carried a basket of lobsters. She, grateful that this enemy soldier had shown her a small courtesy, smiled her thanks, but afterwards, when she was safely past him, she crossed herself. The soldier’s face had been bleak and scarred; darkly handsome, but still a killer’s face. She blessed her patron saint that her own son would not have to face such a man in battle, but had a secure, safe job in the French Customs service instead.

The soldier, oblivious of the effect his face had, found the blue door beneath the green tiles. The door, even though it was a cold day, stood ajar and, without knocking, he pushed his way into the front room. There he dropped his pack, rifle, and saddle-bags on to a threadbare carpet and found himself staring into the testy face of a British Army surgeon. “I know you,” the Army surgeon, his shirt-cuffs thick with dried blood, said.