Entering the chamber alone, even knowing what it held and knowing my own affinity with it, was a very different matter from entering it with Abu. The tunnel appeared longer and darker as I crept along it. I had a light from my wand, but it did not seem to shine far or to illuminate much. Once again, I was aware of that hissing whisper, although now I could recognise it as the voices of serpents.

Half my fear was of Torhild. I did not think that anyone had seen me slipping out this time, so I hoped that she would not follow me, but I knew she had powers I could not guess at. And what if she guessed, when I returned, where I had been? Some old words of Abu's echoed in my mind – Torhild of the Fen makes a good friend, but I think she would make a bad enemy. I did not doubt the truth of that, and I did not want to make an enemy of her. Would she count my disobedience as treachery?

Perhaps not, but what I was planning was certainly treachery.

For the moment, though, I was alone and safe enough. In the central chamber, I carefully cast a protection upon the doorway. Abu should have thought of that last time, but then it would not have made much difference, for we should have had to come out in the end. And so would I, but at least this way there was no risk of being caught unawares.

That complete, I laid my wand, still shedding its yellow light, on the floor beside the casket in the centre. It cast strange shadows upon the ceiling, and left the top of the casket in darkness. But I did not need to see the carvings to know that they were there. Slowly, I put my hand upon them.

The hissing rose around me.

"Sssssnake talker… Why have you returned? Why do you wake ussss?"

"I need to ask you," I whispered, my own hissing joining theirs. "I have to know the truth. Who was he? The man who carved you here. The man buried in the tomb. Is he beyond the door?"

For a moment, their words were lost in a general murmur. I waited, trying to clear out my mind and listen. Rather than speaking in one voice, it was as if they were all attempting to speak to me at once. Frowning, I concentrated.

"The maker… He speakssss of the maker… The great one… The ssserpent lord and his lady sssleep... He at the tail and she at the horn..."

I was little interested in the serpent lord's lady, and I broke in.

"Tell me. Tell me how I can wake him. What secrets did he leave here with you?"

They must know something. Something that would help me outwit Torhild.

"Ssssecretssss..." they hissed to themselves. "Secretsssss, the sssnake talker asssksss. But we only hide the whin-stone bowl. The sssecret wordssss lie elsssewhere for one sssuch assss you to find..."

I thought of Torhild's manuscript. That must hold the secrets they spoke of, and that meant it must hold the secret words too.

"Someone else has it," I told them. "Someone who isn't a snake talker."

There was another general hissing, and I had to wait for them to say anything I could understand.

"They cannot usssse it," they said at last. "Only a sssssnake talker may ssspeak the wordssss. Only for a ssssnake talker will the ssssspell work, for it issss in our tongue.

My heart leapt at the revelation. Only a snake talker. Torhild could not perform the spell herself. Did she know that? Perhaps that was why she wanted me.

"The potion," they went on. "He brewed the mix lit the sssssilver flamessss beneath it, and he sssspoke the wordsss of the great ssspell. And then he called her name and she rosssssse from the bowl like missssst from the marshessss..."

This was it. This was the knowledge that would help me stop her. Only I could speak the spell, and so I could also choose the name to call. My breath caught in my chest at the thought. But I was still missing one important thing.

"What is his name?" I whispered.

For a moment, the chamber went silent. Every hissing voice ceased, and I almost panicked, thinking I had driven them away somehow. But then the sounds returned, more quietly than before.

"Oncccce…" they breathed. "Onccce he wasss called Ssssslytherin…"

And so I heard that name for the first time. Heard it in the soft hissing of a hundred voices, standing in the half-dark of an underground tomb. My heart thrilled with it, and under my breath I repeated it.

"Slytherin."

I emerged from that place blinking in the light, and filled with half-formed plans. My head sang with my new knowledge. Not as much as I had hoped for, but I felt sure that I now knew things that Torhild did not. I alone knew his name, and I stored it in the secret part of my heart.

If I was to be the one to say the words of the spell, there was a chance I could trick her, but I would have to be very clever about it. Torhild saw too far into people's minds. When she looked into mine, it must be filled with dutiful or trivial thoughts. The rest must be kept locked far down inside, for I was sure that if she suspected, she would kill me.

And so I went on with a new purpose. I no longer found my work with Torhild dull, for I reminded myself of the man called Slytherin, who lay within the tomb, awaiting my call. I did not dare to risk another visit to the tomb alone. My first had gone undetected, but I might not be so lucky a second time. I must not arouse suspicions.

I went back only once more, and that was with Torhild. It was time, she said, to begin the formal preparation of the potion, and that must be in the cauldron. She bade me touch nothing but the lid of the casket to open it, and I did as she told me. The snakes moved and hissed, but they spoke no words. Torhild did not understand the snake language, but it was best to be safe, and I kept my own tongue still. The casket open, it was she who lifted the cauldron out with careful hands. Once I saw it properly, I saw that the snakes had spoken more truly in calling it a bowl. It was a simple thing, not metal as I had first imagined, but carved from stone, perfectly smooth and round. The rock was dark, and polished to a dull sheen, the carvings around it representing serpents and other beasts. The whin-stone bowl, the snakes had called it, but I did not know what that meant.

Torhild installed it in the centre of her chamber, upon a pedestal, and it became the focus of our work. I had never seen the brewing of a such a complex potion, even in my work with Abu. Sometimes Torhild frowned and muttered over it in Norse, and I wondered whether she was then regretting driving Abu, with his potioneer's skill, away from her. However, work went steadily on, although we often added nothing to it for months at a time, as it brewed and bubbled. I was not permitted to touch it, only to assist with the preparation of ingredients, and for that I was mostly relieved.

The potion itself was a strange, sinister thing. Mists rose from it at times, and strange shapes appeared in the dark grey liquid. On one occasion, as I followed her into the chamber, she stopped dead and flung an arm out to stop me too. Rising from the bowl was a shape like a cowled monk, although far too thin and elongated to be a human. Torhild uttered a spell, and the chamber lit up with light. I was dazzled, and by the time I could see once more, the thing had gone.

"What was it?" I asked her, breathless with fright. "What was that thing?"

She looked at me. "Such a potion brews strange things in its depths," was all she would say.

I wonder now whether she knew herself what it was. I suspect not.

The mood in the halls changed. I was not sure who among her servants knew what we did in her chamber, but I could not ask. People became quieter. Those who had been readiest to smile and exchange a friendly word now seemed quiet and more anxious. There were strange outbursts of anger from some, but most were simply withdrawn. I myself paid little heed to it. More and more, I was caught up in my own doings, my plans and my studies. It suited me well enough to be left alone.

And so I reached, by the count I kept and by my own reckoning now, my fifteenth year.

One day early in that year, as the winter began to fade and touches of green to appear again around the marshes, I received a letter. The hawk came sweeping into the hall as we supped, and dropped a rolled parchment before me. My first that was that it would be from Helga, although her letters were less frequent in those days, or even from Abu, who wrote to me occasionally with well-wishes and notes on some new potion. But it was not in Helga's careful script, nor yet in Abu's Arabic hand. It was in untidy English, and I knew from the first sentence who had written it.

To my brother Salazar,

I hope you are well. Beorhtric heard from Abu al Sadiq of where you dwell now, and so I write to you to tell you that soon I will be riding close by your doors. My father goes north, to attend the king's business in Northumbria, and I ride with him. We shall pass close by the fenland, and I propose to come and see you. You can send the hawk back with a reply and she should find me, but we are already on the road, so if I do not hear word before we are close, I shall come without invitation. It has been too many years.

I also have a proposition for you – ride north along with us. My father should be glad to have you, and you have been long enough in the fens. Besides, I do not imagine your sword skills have improved any, so I can continue your lessons. Think on it, Salazar.

Your friend,

Godric

My mouth curled into a rare smile as I imagined him penning the letter. I could hear his lordly tone in the words, although he would not be the little boy I left him, any more than I was myself.

Before I could have any other thoughts, the letter flew out of my hands, and I glanced up in time to see Torhild snatch it out of the air. I glowered at her, but there was little I could do as she read through it.

"So." She looked down at me from her place at the head of the table. "Your young friend comes to visit."

I bit back the annoyed reply I wanted to make. "Yes. May I receive him here?"

She smiled thinly. "You may. After all, it seems he is coming, invited or not, and we do not turn visitors away from our gates. Even Saxons. And will you do as he wants and leave with him, Salazar?"

By now a number of other people looked interested. Ulf was staring at me, his face impassive. I ignored him and looked at Torhild.

"No. I shall stay here."

The thought of riding away with Godric was tempting, but there was too much still to be achieved in the fens. I had helped to put things in motion, and I must see them to the end.

Her smile grew a fraction. "Your loyalty is commendable."

I stared at the table, allowing no thought of my real plans to surface in my mind or show on my face. The letter floated back to me, and nobody said any more on the matter. But that night I penned a letter to Godric telling him to come to Torhild's halls, and sent it off with his hawk, after I had fed and watered the bird, and allowed it to rest. And over the following days, I thought often of Godric's coming visit, and felt cheered by the prospect. It had indeed been too many years.

It was not long after that that Torhild told me that the potion was ready.

Thoughts of Godric were at once driven from my mind. I spent a night in wakeful terror, for I had planned for this so long, but now it seemed impossible. I did not doubt that the potion would work, but how could I, just a boy still, hope to outwit Torhild of the Fen? Even Abu had not been able to.

But Abu had not lived with her for five long years, I told myself. Abu had not known the things I now knew. I must attempt it, for it might be my only chance to meet the man called Slytherin. Already, privately, I had begun to use the name myself, inscribing Salazar Slytherin upon the books that were mine – mostly left to me by Abu – and to imagine myself in some way his descendent. His heir. Of course, I knew that I could not be, but it was a fantasy I preferred to the knowledge of my real descent.

Besides, it was also my only chance to stop Torhild's plan of plunging Britain into a war of the kind it had not seen for decades. Not that I cared much for most of the people who would suffer, but I did care for Godric, and he was a Saxon, one of those she hated.

At the time she had commanded me, I made my way to the main hall. Torhild was there ahead of me, and with her was Ulf. I paused in the doorway, for they were standing at the far end of the hall, close together, and their voices, although low, were angry. I still knew only the odd word here and there of Norse, mostly spells, and I could not understand their rapid speech, but I could tell that they were arguing. Ulf had grown no more friendly to me in the years that I had dwelt on the fens, and I was loath to interrupt them.

They were too much engrossed to notice me. I stood and watched as their voices rose – or rather, as Ulf's voice rose, for Torhild remained cold and steady. At last, after a final outburst, he turned on his heel and stalked out of the room.

I had too much to think of to let my mind dwell on it, however.

My only plan – and I realised then how thin a plan it really was – was that when it came to the moment of speaking the names of those Torhild wished to raise, I would instead call upon the great wizard, Slytherin. If I could summon him, he and I together would be a match for Torhild. What would happen next, I had no idea, although I had created many fantasies of the man adopting me as his son and heir, of us ruling the fens together. I also had no idea what would happen should I fail, and I shivered at the thought of Torhild's anger. I must not fail, that was all.

Torhild, on the other hand, seemed to be quite sure of her plan. She had never told me the details of it, though, and still she was silent as she gathered this and that from around her chamber – the vellum manuscript with her instructions in it, her own parchment notes, her wand, a silver knife, and of course the cauldron itself, in which lay the precious potion. I myself had my old knife tucked away in my belt, hidden under my wool cloak along with my wand. I did not intend to use it, but I felt safer with it there, for all my developed skills with a wand.

"Come," Torhild said to me at last.

I followed her from the chamber and through the great hall, which was deserted. Dusk was falling, and we went out on foot, the usual night mist lying low over the marshes. There was no sign of Ulf.

"Where are we going?" I asked.

I was, as always, feeling annoyed at how little she told me, although I told myself I should not care, given that my plan was to betray her. Then again, if I let myself feel annoyed, perhaps she wouldn't notice any of my other emotions.

"To the marsh of the dead," she said, without looking at me.

I had heard of that place, but I did not know where it was, even though I knew all the marshes around Torhild's home. An old resting place for Norse warriors of a past age. The people Torhild planned to wake. I was struck with unease. Must the spell be performed where the dead were buried? The snakes had not said so. And surely the tomb would be close enough anyway. It might be just that Torhild felt it an appropriate place, for she liked symbolism.

As we walked further out, I began to wonder how far away this marsh was. Dark set in properly, and the moon rose, large above the horizon. Torhild, for all her age, showed no signs of weariness. I struggled after her in the dark, my wand lighting the way but still leaving shadows and dark hollows for me to stumble in. At last, she stopped.

"Here," she said.

I looked out. We stood at the edge of a marsh that was almost a lake, for water stretched out a long way before us, and in the light we cast I could not see any banks or trees in it, only the path of the moon glimmering in its ruffled surface. I might have been to this place before, but in the dark it was hard to tell. There were no markers to show that it was a resting place of the dead.

"Here?" I echoed.

"Here is where my sisters lie," Torhild said, staring across the water. "Here we set them upon barques, all six of them in their time, and lit the pyres. I stood in this spot and watched the flames consume them, and the boats sink into the marsh. Here is where we begin the great task in store."

As I watched, she began to prepare. Around us, she cast a protective circle, and then in the centre she lit a fire, upon which she placed the cauldron. The flames of the fire burnt a pale ashy colour, and I recalled the words of the snakes in the tomb. The silver fire.

Torhild lifted her arms and spoke the words of some strange enchantment that made the hairs on my neck prickle. Then she turned to me.

"It is time," she said. "Come, boy."

As if in a dream, I came to her. She crouched and laid out the parchment on the ground, and I knelt beside her. In the dim light, I could see the writing on the parchment, but it was like nothing I had ever seen before. The letters were a series of curves and loops more like Arabic than like the angular English marks, but it was not Arabic. As I looked, though, I found that I could read the words. I knew then what it was, although I had not thought such a thing possible – it was the snake tongue, but rendered in writing. And I knew what this must be, and knew also what Torhild wanted of me.

"Read it," she commanded.

And so I did. I spoke the words in the snake tongue itself, and as they passed my lips I felt the power of them. I had never uttered words of such power before, nor heard them uttered, and it seemed to me as though the air was filled with a charge like that before lightning strikes. I almost forgot Torhild, and the marsh, and even the dead Norse witches under the water, until I came to the end. The final syllable fell from my tongue and I was aware again of where I was, could smell the mud and feel the breeze against my cheek.

I was breathless, as if I had been running. But it was not finished. Something was missing. It was waiting for something. The name? Was it time to speak the name? But even as my tongue hesitated upon it, Torhild broke in.

"Good. And now your part is almost done. But one last thing is required. One last ingredient to be added after the spell has been spoken. The blood of a snake talker."

I stared at her, and perhaps it was the near-trance state I had been in that made me take so long to understand. If I had been quicker, I might have been able to defend myself. But her wand was on me, she spoke a harsh word, and suddenly my limbs would not do my bidding.

In shock, I stared at her. "What? What do you mean?"

"I'm sorry, boy. But I need your blood."

In her hand, she held the silver knife, and terror washed through me like a cold tide. In all my plans and schemes, I had never considered such an end. Why had my little snakes not warned me? Why had Abu not realised, and refused to leave me here? Had this been her plan all along? She was going to kill me, here in the marshes, and I would never see Godric again, or Helga or Abu. She would raise her army and I would neither be able to stop her, nor ride with her at its head. Fear froze me almost as surely as whatever spell she had cast upon me.

"Torhild, I... Please, don't!" The words came rushing from my tongue, not caring for the shame of pleading. I only wanted to live. "I'll give you my blood; you can have it! Please don't kill me!"

Her eyes were lit by the same pale fire that burned beneath the cauldron.

"Not kill you? Yes, I could take your blood and spare your life, but why should I? Do you think I do not know your treachery? Do you think I do not see every secret thought within your heart? Snake talker? You are the serpent yourself, and I shall stamp you out like the little poison adder, Fernando Salazar."

The blade flashed, but in the moment I had given up all hope, a voice spoke, loud and harsh in the night air.

"Let him go, you old hag! Let him go!"

I could only twist my head, but Torhild swung around. And there, standing upon the path we had come along, was a figure in the darkness, tall and cloaked. I could not see his face in the darkness, but before him flashed the long blade of a sword, and I knew the voice. My heart leaped with sudden desperate hope. Godric had come for me.