I could only stare at the dead boy's face, unable to frame a single thought.

'Can't you see?' Vigilantius snapped. 'Everything is different here.'

'Note the position of the legs,' Professor Kant continued, ignoring both of us, completely absorbed in what he was doing. 'The others were kneeling when they were murdered. This boy was not. You saw the position of the body of Herr Tifferch last night. Now you have room for comparison. I instructed the soldiers to conserve his corpse under the snow for you and the doctor to examine.'

So, there it was. The answer to the question with which I had been plaguing Koch. Professor Kant had been behind it all. He had arranged and orchestrated every move that I had made since reaching Konigsberg. He had sent me to see Herr Rhunken, who was not expecting me. Then, I had been directed to the horror chamber of Vigilantius. Kant had decided that I ought to lodge at The Baltic Whaler. The police had had no say in the matter. Nor had the King. Immanuel Kant knew more about those murders than any man in Konigsberg.

'Let's see if Vigilantius is right,' he said. 'Turn the boy on his stomach, Herr Koch. If you would be so kind?'

Koch lay Morik gently face-down in the mud. The boy's hair and neck were caked with blood and mud. 'Bring water, Sergeant,' Kant urged, and Koch sped off towards the bridge, returning with a metal water bottle he had taken from one of the soldiers.

'Douse his head,' Kant instructed. 'Pull back the hair. Remove that mud.'

He directed Koch's attentions with the firmness he might have used to guide the hand of his laboratory a.s.sistant at the University. 'More water. Clean the neck. Yes, there, there!' Kant pointed with impatience.

As the blood and the dirt drained away, white flesh emerged. Kant leaned forward and stared intently at the b.u.mpy vertebrae of the boy's neck. 'There is no wound here. No sign of it at all. The injury to the skull was done with a hammer, or a heavy object. It ought to have bled copiously, and yet I see no sign of blood here on the ground.'

'The cold might have staunched the bleeding,' I suggested.

'The temperature cannot explain the absence,' Kant snapped with a flash of irritation.

'What would you suggest then, sir?' I asked.

'He was not killed here. Nor by the person that we are seeking. The evidence is quite plain,' he replied. 'This boy was killed for a different motive, whatever it may have been.'

I was bewildered. Kant had reached the same conclusion as Vigilantius.

'But there cannot be two murderers in Konigsberg!' I protested. 'Morik was killed at the inn. I saw him there. His body was left here to throw me off the trail. I have every good reason to believe that he knew something about the other murders. Why, I spoke to him last night!'

Kant's eyes sparkled with excitement. 'You spoke to the boy? Do you mean to tell me that you arrived at the inn and immediately won his confidence? Well, that is truly remarkable! I was right to choose you, and correct again in sending you to The Baltic Whaler.'

For a moment, I believed he was teasing me. Then, I thought, perhaps he was genuinely impressed. He had placed me there for no other purpose, after all. 'That tavern is a hotbed of spying and sedition,' I said. 'But you knew that already, sir, didn't you?'

Kant looked at me, and I'd swear there was a mischievous twinkle in his eye.

'Your arrival must have caused some tension,' he observed quietly.

The events of the previous evening at the inn flashed before me. The anger on Herr Totz's face, the suspicious behaviour of his wife, the boy's terror of them both. I told Kant everything that Morik had revealed about the foreigners staying there, and added what I had seen from my bedroom the night before.

'It's just as Procurator Rhunken suspected,' I said. 'Insurrection. Foreign agitators. What better motive could explain these murders?'

'I could postulate a hundred,' Kant replied immediately. 'One certainly comes to mind.'

He gazed at the River Pregel, as if the dark waters were an aid to concentrated thought.

'I beg your pardon, sir?' I asked timidly.

'The sublime pleasure of killing, Stiffeniis,' he replied slowly, carefully separating his words.

I was amazed. Had I heard him right?

'Can you be serious, sir?' Sergeant Koch burst out. 'Excuse me, Herr Stiffeniis,' he apologised, 'I did not mean to interrupt.'

'I appreciate your frankness, Herr Koch,' Kant replied. 'Go on, Sergeant. Say what you feel compelled to say.'

'Could any sane person kill for such a reason?' Koch demanded. He did not seem to be the least intimidated by the mighty reputation of Immanuel Kant. 'For pleasure, and nothing more?'

Kant studied him quizzically for a moment. 'Have you ever been to war, Sergeant?'

Koch blinked and shook his head.

'But you do have friends or acquaintances in the army?'

'Yes, sir, but...'

Kant raised his hand. 'Bear with me, Koch. If you were to object that killing an enemy on the field of battle is a question of duty, I would not dispute it. But there is an ambiguity in doing the deed which may be worthy of our consideration. I have met few soldiers who are ashamed of their murderous capacities, or reticent in claiming to have perpetrated the most exquisite savagery in the sacred name of duty. And not on the field of battle alone. Duelling is common among the officers in our army.' He nodded down at the corpse. 'A man who possesses these lethal skills may find untold pleasure in using them.'

'A soldier, sir? Is that your theory?'

Kant directed his attention to me, as if Koch had never opened his mouth.

'Imagine the power of life and death in the hands of this person, Stiffeniis! He chooses the victim. He chooses the time, and the place of the execution.' He counted off these circ.u.mstances on his thin white fingers. 'Only G.o.d has such unbridled power on this Earth. The act of killing may be a source of immense power, of gratification in itself, but that is not the end of it. Look over there,' he said, pointing across the river at the crowds lining the opposite bank. 'Look at the soldiers manning the bridge. Consider our presence here, the terror that moved the authorities to summon us. Whoever he is, whatever his motives may be, this person has unleashed Chaos in Konigsberg. He commands us all!'

'Power, sir?' Koch insisted with a frown. The hypothesis seemed to alarm him more than any other possibility.

'A power which accepts no human limits, Sergeant Koch. A Deity. Or a Demon, if you like.'

A cold wind swept over the waters of the River Pregel. When Doctor Vigilantius spoke, his voice sounded as sharply as the first crack of the polar ice-cap in Spring.

'Professor Kant,' he said. 'I can do no more for you, sir. I have urgent business to attend to. If you need me again, you know how to contact me.'

'Your a.s.sistance has been of incalculable value in this affair, sir,' Kant replied with all the respect he might have employed if David Hume or Descartes had been present. 'Stiffeniis will make good use of your findings.'

With a final, dismissive glance in my direction, Augustus Vigilantius, that glowing meteor of the Swedenborgian universe, turned and walked away along the river bank, never to appear again in Konigsberg while I was there, except in the columns of Hartmanns Zeitung. His 'urgent business' turned out to involve a conversation with a billy-goat, the animal having been possessed by the soul of the farmer who had once been its master.

Kant smiled warmly at me. 'I hope we'll have no further need of him,' he said. 'Now, regarding your conspiracy theory, Stiffeniis. You should verify it.'

I was taken back. 'I thought you did not share my opinion, sir?'

'It is your theory, Stiffeniis,' he said warmly. 'You must put it to the test. That is the essence of modern scientific methodology. Go at once to the Fortress and interrogate those people from the inn. When you've finished, there is something I would like to show you.'

'Excuse me, Herr Stiffeniis,' Koch intervened. 'What about the fisherman who found the corpse? You'll need to speak to him, sir.'

Before I could reply, Kant turned sharply on Koch.

'Don't waste your master's time! That poor fellow knows nothing, I am sure. I'll pick you up at four of the clock,' he said to me as he turned away towards the bridge. After a few halting steps, he looked back with an enigmatic smile. 'Aren't you curious to know more about the Devil's claw, Hanno?'

He did not wait for my answer.

'I am at your disposition, sir,' I murmured, watching in silence until he had safely reached the stairway to the road. Then, I gave orders for the body of Morik to be removed, waiting while the soldiers went about the sad business. As they covered his face, I recalled the fawning smile of Frau Totz and her pretence of concern for the child that morning. A wave of anger swept over me.

'To the Fortress, Koch,' I snapped. 'It is time to loosen some tongues.'

Chapter 12.

Koch glanced around the room with a show of concern. 'I had your personal belongings brought here from the inn,' he said. 'It was the best I could do at such short notice, sir.'

The accommodation on the first floor of the Fortress was tiny. There was just s.p.a.ce enough for a narrow bed and a wooden chair on which my travelling-bag had been placed. The acid taint of stale urine from a cracked porcelain night-bowl peeping beneath the cot hung heavily in the air. A window high in the wall provided next to no illumination, and it was icy cold in there. No one had taken the trouble to light the stove. The screaming and shouting of the prisoners down below was muted, which was a relief, but had a turnkey come along and locked us in for the duration, I would hardly have been surprised.

'It will do well enough,' I said with less animation than I truly felt. I had taken possession of Procurator Rhunken's private chamber, the room he used for resting when the pressure of work denied him the comfort of returning to his own house. I glanced at the four walls as if to familiarise myself with their grey drabness. 'This is where I should have been lodged in the first place,' I added with the conviction of an anchorite examining the cave in which he was destined to spend the rest of his penitent life.

'You did make some important discoveries down at The Baltic Whaler, sir,' the sergeant reminded me.

'We should be thankful for small mercies, I suppose.'

'Professor Kant seemed pleased,' Koch continued, though his tight-lipped manner gave the lie to the compliment.

'Is something bothering you, Koch?'

He did not try to deny the suggestion, tugging at his shirt collar as if the room were ten degrees warmer than it was. 'A couple of things, sir,' he began with some hesitancy. 'I was wondering about Professor Kant, sir.'

'What of him?' I asked brusquely.

'I was most surprised to find the gentleman down by the river this morning, sir. At his age, it seems rather odd that he should take such a...morbid interest in murder. Don't you think so, sir?'

'He is not vulgarly interested in murder, Koch, if that is what you mean,' I replied quickly, for the sergeant had given voice to a perplexity which I shared. 'Herr Professor Kant cannot countenance the disorder that crime brings, that's all. He fears for Konigsberg and would suffer any inconvenience for the city that he loves.'

'Nevertheless, he did not seem to share your theory about a revolutionary conspiracy being the cause of these crimes,' Koch went on.

'Professor Kant is neither a magistrate nor a policeman,' I explained. 'He did concede that it seems to be the most obvious explanation. He is the supreme theorist of Rationalism in Prussia. He wants a hypothesis that can be confirmed by solid evidence. When we meet him again this afternoon, I intend to provide the definitive proof that he seeks.'

'Indeed, sir,' said Koch. He did not sound entirely convinced.

'And the other matter?'

Koch placed a hand on his vest as if to calm the beating of his heart or apologise in advance for what he was about to say. 'It concerns your brother, sir,' he said. 'Herr Kant spoke of him in connection with that boy this morning. Was your brother murdered, sir?'

I half turned away, opening my bag, pretending to look for something.

'Not murdered,' I snapped. 'As I told him, Sergeant, it was an accident. A most unfortunate accident.'

I rifled through the contents of my bag to avoid his gaze. When I looked up again, I thought I caught an expression of bewilderment on Koch's plain face. Brushing past him, I strode through to the connecting room.

'Where are the prisoners?' I asked.

'Officer Stadtschen is waiting on your orders before he brings them up, sir,' Koch replied, straightening his jacket, his face a neutral mask once more.

'Ask him to step in on his own first, would you?'

As if I had called the Devil, the Devil came. There was a sharp rap on the door, and Stadtschen presented himself with a stack of papers in his hands. He was an enormous man with a bloated red face, resplendent in an immaculate dark blue uniform with white stripes on his sleeves and along the seam of his riding-breeches. 'Foreign visitors in Konigsberg, sir,' he said with a bow, handing me a copy of the list of names that had been drawn up for General Katowice.

I took the paper from him and scanned the names.

'Twenty-seven persons? In the whole of Konigsberg?'

'We don't get many outlanders these days, sir,' the Officer replied. 'There are sailing-ships, of course, but they come and go the same day, most of them, or the crews sleep aboard. Casual visitors avoid the city, sir. No sensible man wants to get himself murdered.'

'Are any of the names on the list known to the police?'

'No, sir. I checked them myself.'

I noted the names of the three gem-traders who had been at The Baltic Whaler the night before. 'You searched the inn, did you not?'

'Indeed, sir,' he said, placing a large bundle of papers on the desk before me. 'This is a sample of the material we discovered there.'

'Where was it hidden?'

'In a secret room, Herr Procurator. A trap-door beneath the carpet in one of the upstairs bedrooms.'

The image of Morik spying came back to me. Was that what he had been trying to communicate to me the night before? That a seditious meeting was going on in that room opposite my window?

'Papers and maps, sir,' Stadtschen went on.

'Maps?'

'Of Konigsberg, sir, and other places, too. And pamphlets written in French. The name of Bonaparte figured large in the texts.'

'Did you find any weapons?'

'None, sir,' Stadtschen replied with a grin, 'except for an old pistol in the bedchamber of Totz. It's as rusty as a lost anchor and would blow up in the face of anyone rash enough to fire it.'

'How many persons did you arrest?'

'The landlord and his wife only. Those tradesmen that Sergeant Koch said you were interested in had left the city early this morning. They may have left by sea. The gendarmes are trying to trace them now.'

'Did Totz or his wife say anything at the moment of their arrest?'

'I didn't pay them much attention, sir,' Stadtschen replied. 'I had more important business to attend to.'

'What do you mean?'