‘Why did he leave the orphanage?’

‘He stole out on the night of his death. His friends don’t know where he was headed, but he had taken all his meagre belongings so he had gone for good. It’s an astonishing coincidence: as soon as I return, there’s another murder.’

‘I don’t believe in coincidences,’ declared Margont.

‘Neither do I.’

‘So what’s the link between the two events?’

‘I can’t answer that question yet, although I keep asking it myself.’

‘We will have to try to find the people who investigated Franz’s death.’

Relmyer gritted his teeth to prevent himself from letting loose a stream of vituperation. The merest mention of the Viennese police made him want to hit something — the trees, the houses, the world. For a few seconds he was unable to reply. ‘I’d already thought of that. As much as it pained me, I did make the effort to try to see those incompetent imbeciles, but I failed. One died last year of inflammation of the lungs. Two others joined the Viennese Volunteer force and were subsumed by Archduke Charles’s army. The last one fled before the troops arrived. And to top it all off, when the police were evacuated from the capital they took most of their archives with them ...’

Relmyer raised his chin and looked at Margont with sparkling eyes. He regularly forced himself to appear cheerful and sometimes even felt it. Changing the subject, he added: ‘I like the way you put things. Very clear, very mathematical.’

‘Really? “Mathematical”?’ Margont had never heard the word used as a compliment.

‘Do you like maths?’ asked Relmyer.

‘Not much.’

‘That’s a great shame! Maths is at the core of everything, it is the very essence of the world. It enables us to translate the complexity of what surrounds us into a simple, codified language.’

‘The essence of the world?’

‘The trajectory of a cannonball, the dome of a cathedral, the strength of a bridge, the speed of movement of an army, a series of attacks in a duel ...’

‘And that’s what you think the world is? What about love, friendship, literature? Also just maths?’

‘Not yet, but one day, certainly.’

Margont did not agree with this point of view and wanted to respond, but Lefine intervened with the consoling words: ‘Not to worry, Captain, we won’t be around to witness that sad state of affairs. The war will have killed us long before.’

The little group stopped on the banks of the Danube and the

horses hastened to drink from the river. Behind them, the French troops and their allies were arriving at their quarters. Large shapeless masses, topped with a forest of muskets, moved slowly across the plains. The noise of their displacement, the muted hammering of thousands of steps and the clanking of arms and other equipment sounded almost ferocious. Messengers went to and fro at the gallop. The march of these titanic centipedes could be halted by three virtually illegible lines scribbled by an aide-de-camp trying desperately to take down orders rapped out by Napoleon. They would then be sent in a different direction.

‘Look at all those islands,’ commented Relmyer.

The majestic course of the Danube was indeed sprinkled with an astonishing number of small wooded marshy islands, covered with tall grasses ... impossible to tell with the naked eye what their topography was like.

‘Without even counting the part of the Danube that runs north from Vienna or south from Lobau, which is the largest island, you can see hundreds of them - they look like a labyrinth. The vagaries

of the current either throw them up or obliterate them. I don’t know why Wilhelm and the man we’re hunting would have come here. But I know one thing: if you knew this area well, you could easily lose yourself in it, even if fifty soldiers were on your trail.’ ‘Which of these islands were they on?’

Relmyer’s gaze sought Pagin, who was investigating the river, his horse submerged up to the chest. He was imagining himself parading in front of the Emperor, to announce that he, Pagin, of the 1st Squadron of the 8th Hussars, had discovered a ford across the river. No more pain-in-the-neck bridges collapsing! Unfortunately, others before him had searched and failed, and before long he would be swept away by the current, waving his arms in agitation. These days, it was always the Danube that had the last word. Relmyer signalled to him and Pagin came galloping back. The affair distressed him. He would dearly have loved to solve it for the two officers.

‘It’s impossible to tell, Lieutenant. I was able to interrogate only second-hand witnesses and they contradicted each other. It was

somewhere here, not far from Vienna, during the night of 19 May. The patrol was following the river when they heard a noise and saw two silhouettes on the one of the islets. They shouted out and then fired ... In the time it took them to commandeer a boat, the other fellow had disappeared.’

‘Was the boy wet?’

‘Soaking.’

Relmyer, pensive, stroked his horse’s neck. They must have wanted to swim across. The bridges have been destroyed in several places by the retreating Austrians, and Archduke Charles has sabotaged most of the boats.’

Margont let his gaze slide over the surface of the water, seeking out the shimmers that caught the rays of the sun. ‘The Danube’s currents make it dangerous to cross. They must have gone over at night to avoid being seen by the sentries. And our man must have taken care to keep his pistol dry; he probably hid it under his hat. He would have been able to make use of the confused mass of islands to conceal their escape. Would you know how to do that?’

Relmyer shook his head. ‘I don’t think so.’

‘So he knew the lie of the land even better than you. How did he meet Wilhelm? What did he do to persuade him to come as far as this? Where were they going? And for what? There are so many unanswered questions.’

Relmyer gave a bitter laugh, but it seemed to hide the salty taste of tears. ‘So many unanswered questions? That’s all I have, questions! Who is this man? Why does he mutilate his victims? How long will he go on killing? And how can we stop him?’

They frittered away several minutes trying to work out the exact spot where Wilhelm had been assassinated. They tried to find a boat first, but all the boats not already swiped by the Austrians had been requisitioned by the French. Pagin insisted on plunging into the water, bolt upright on his horse. The current bore him away and his horse began to turn its head from side to side, searching for firm ground. Finally the animal succeeded in reaching one of the little islands, but it was not the one Pagin had been aiming for. Despite his best efforts the hussar was only able to

explore half a dozen islands.

Finally Margont exclaimed in exasperation, ‘It’s like looking for a needle in a haystack!’

‘Even an entire regiment wouldn’t be enough to find the island,’ admitted Relmyer.

Pagin painfully made his way back to the riverbank, exhausted and trembling, and delivered his conclusion: This man knows the area like the back of his hand.'

Lefine clenched his teeth. ‘We knew that already before wasting three hours here.’

Margont turned towards Relmyer. ‘Why don’t you show us the cellar you were locked up in?’

‘I don’t think we have time, it’s already late ...’

Late? It was midday! Relmyer wanted to return to the cellar, but at the same time he would have given anything never to have to set foot there again. ‘All right. I’ll take you,’ he conceded with bad grace.

They followed the banks of the Danube back towards the north-west. Then they skirted round Vienna to the north. Neither Lefine nor Margont had managed to visit that admirable city at the time of the 1805 campaign. All the riders except Relmyer looked towards it, avid to discover the least little detail about it even from afar. They lost time because there were troops in their path. The battalions had become muddled up trying to get round a mass of ammunition wagons. The light horse of the Imperial Guard, arriving in their turn, had decided to take the shortest route and simply galloped through the infantry. Bad idea. The resulting disorder rang with shouts, threats and injunctions. Behind this chaos could be seen the hand of Napoleon.