She was thirty, and she had buried her youngest son that spring. Now she had to flee the army marching towards her home. Its commander entered her capital in triumph. He was already telling Europe that the war was her fault.

On 27 October 1806, Napoleon rode into Berlin through the Brandenburg Gate. Queen Louise of Prussia was elsewhere, caught up in the flight that followed her country's military collapse. Thirteen days earlier, the Prussian armies had been defeated at Jena and Auerstedt. French troops had entered Berlin before their emperor; now came the ceremonial procession. The queen whose presence had helped make the monarchy popular had gone, and the conqueror had arrived.

Louise had married the future Frederick William III in December 1793, when she was seventeen. He became king four years later. Their marriage offered their subjects something unusually easy to recognise in a royal household: a couple attached to each other, taking pleasure in family life. Louise became fashionable, widely represented in paintings and sculpture, a young woman through whom people could feel affection for a dynasty.

That family life had a place away from Berlin. At Paretz, in the countryside near the River Havel, they spent summer weeks with the children, escaping some of the ceremony of court. There were boat trips and rides, games and guests, and the royal household even joined the villagers at their dances. The simplicity was royal simplicity, with a country house and an estate behind it, but the pleasure they took in it was real enough.

The nursery had already lost one child in 1806. Prince Ferdinand, the youngest, died on 1 April, fifteen months old. Five children remained, the eldest ten and the youngest, Alexandrine, three.

In September, Louise appeared before departing troops in a blue dress with a red collar and lapels. These were the colours of the dragoon regiment of which she had been made honorary chief. Her husband was going to join the army, and she went with him to headquarters. She had publicly put herself beside the soldiers and behind resistance to Napoleon. The dress made that allegiance visible.

A queen could lend her presence to an army. She could not make it win.

On 14 October, at Jena and Auerstedt, the confidence with which Prussia had gone to war broke against the French armies. Louise left Weimar that day. Her road ran north through Heiligenstadt, Brunswick and Tangermünde to Berlin, and she did not stay there. On the evening of 18 October, at the palace of Schwedt on the Oder, she was with her children again. Her eldest son had turned eleven the day after the battle. From there the road went on to Stettin and Küstrin, where she found the king. There were still royal titles, attendants and places to shelter. There was no longer a secure capital to return to.

Napoleon's attack followed her in print. His army bulletin of 16 October accused her of continually urging on the king and his generals, of wanting bloodshed, and then pointed to the blood that had been spilled. It was a particularly convenient account of the disaster. The defeated army had commanders, and the kingdom had a king, but the queen could be made the woman who had set them all in motion.

Her public support for the war gave the accusation something to fasten on. The blue dress, the regiment and the journey to headquarters could all be turned into evidence of a woman meddling where she ought to have stayed quiet. Napoleon's bulletins carried his victories to their readers. They carried his version of Louise with them.

She had supported resistance. He made her answer for defeat.

In Berlin, the emperor's entrance supplied the other half of that story. His foot guard marched ahead, cuirassiers lined the route, and city officials came to the gate to offer him the keys. He rode between the grenadiers and the mounted chasseurs of his guard and dismounted at the royal palace at three in the afternoon, where his own grand marshal of the palace was waiting to receive him. A household had left the capital. Another had moved in.

The following summer, in July 1807, she went to meet him at Tilsit. The woman his bulletins had attacked was now being asked to help win better peace terms from him. Hardenberg, one of Prussia's leading statesmen, prepared her for the conversation. Much was expected of her presence and her appeal. She went, and the appeal failed to secure the hoped-for terms. The man who had made so much of her influence in bringing about war gave her no such power over the peace.

Louise stayed away from Berlin after Tilsit. The family's refuge in the east became a prolonged residence, and the return kept receding. When she finally came back to the capital with the king on 23 December 1809, more than three years had passed since the flight, and she was thirty-three. The family was larger than the one that had fled. Two more children had been born in Königsberg during the exile, the younger only eleven weeks before the queen drove home through the city that had watched Napoleon ride in.