But it was far denser than smoke; it looked like water, like a black whirlpool swirling above our heads. Within seconds it became calm and still, resembling the polished surface of a dark mirror. I could even see our reflections in it: me standing next to the Spook, his staff at the ready, blade pointing upwards, ready to jab.

What happened next was too swift to see properly. The surface of the smoke mirror bulged out towards us and something broke through fast and hard enough to send the Spook sprawling backwards. He fell heavily, the staff flying out of his hand and breaking into two unequal pieces with a sharp snapping sound.

At first I stood there stunned, hardly able to think, unable to move a muscle, but at last, my whole body trembling, I went across to see if the Spook was all right.

He was on his back, his eyes closed, a trickle of blood running from his nose down into his open mouth. He was breathing deeply and evenly so I shook him gently, trying to wake him up. He didn’t respond. I walked across to the broken staff and picked up the smaller of the two pieces, the one with the blade attached. It was about the length of my forearm so I tucked it into my belt. I stood at the side of the chain looking upwards.

Somebody had to try to help Alice destroy this creature once and for all, and I was the only one who could. I couldn’t leave her to the Bane. So firstly I tried to clear my mind. If it was empty, the Bane couldn’t read my thoughts. The Spook had probably been practising that for days but I would just have to do my best.

I put the end of the candle in my mouth, biting into it with my teeth, then gripped the single chain carefully with both hands, trying to keep it as still as possible. Next I placed my feet above the hook and gripped the chain between my knees. I was good at climbing ropes and a chain couldn’t be that different.

I began to move upwards quite fast, the chain cold and biting in my hand. At the bottom of the thick smoke I took a deep breath, held it, and pushed my head up into the darkness. I couldn’t see a thing, and despite not breathing the smoke was getting up my nose and into my open mouth and there was a sharp acrid taste at the back of my throat that reminded me of burned sausages.

Suddenly, my head was out of the smoke and I pulled myself further up the chain until my shoulders and chest were clear of it. I was in a circular chamber almost identical to the one below except that, rather than a chimney above, there was a shaft below and the smoke filled the lower half of the chamber.

A tunnel led from the opposite wall into the darkness and there was another stone bench where Alice was sitting, the smoke almost up to her knees. She was holding out her left hand towards the Bane. That heinous creature was kneeling in the smoke bending over her, the naked arch of its back reminding me of a large green toad. Even as I watched, it drew her hand into its large mouth and I heard Alice cry out in pain as it began to suck the blood from beneath her nails. This was the third time the Bane had fed on Alice’s blood since she released it. When it had finished, Alice would belong to it!

I was cold, as cold as ice, and my mind was blank. I was thinking about nothing at all. I pulled myself up further and stepped from the chain onto the stone floor of the upper chamber. The Bane was too preoccupied with what it was doing to be aware of my presence. No doubt in that respect it was like the Horshaw ripper: when it was feeding, hardly anything else mattered.

I stepped closer and pulled the piece of the Spook’s staff from my belt. I raised it and held it above my head, the blade pointing at the Bane’s scaly green back. All I had to do was bring it down hard and pierce its heart. It was clothed in flesh and that would be the end of it. It would be dead. But just as I was tensing my arm, I suddenly became afraid.

I knew what would happen to me. So much energy would be released that I would die too. I would be a ghost just like poor Billy Bradley, who’d died after having his fingers bitten off by a boggart. He’d been happy once as the Spook’s apprentice but now was buried outside the churchyard at Layton. The thought of it was too much to bear.

I was terrified – terrified of death – and I began to tremble again. It started at my knees and travelled right up my body until the hand holding the blade began to shake.

The Bane must have sensed my fear because it suddenly turned its head, Alice’s fingers still in its mouth, blood trickling down its big curved chin. But then, when it was almost too late, my fear simply evaporated away. All at once I realized why I was there facing the Bane. I remembered what Mam had said in her letter…

‘Sometimes in this life it is necessary to sacrifice oneself for the good of others.’

She’d warned me that of the three who faced the Bane, only two would leave the catacombs alive. I’d somehow thought it was going to be the Spook or Alice who would die, but now I realized that it would be me! I was never going to complete my apprenticeship, never going to become a spook. But by sacrificing my life now I could save both of them. I was very calm. I simply accepted what had to be done.

I feel sure that at the very last moment the Bane realized what I was going to do, but instead of pressing me dead on the spot it turned its head back towards Alice, who gave it a strange, mysterious smile.

I struck quickly with all my strength, driving the blade towards its heart. I didn’t feel the blade make contact but a shuddering darkness rose before my eyes; my body quivered from head to foot, so that I had no control over my muscles. The candle dropped out of my mouth and I felt myself falling. I’d missed it’s heart!

For a moment I thought that I’d died. Everything was dark but for now the Bane seemed to have vanished. I fumbled around on the floor for my candle and lit it again. Listening carefully, I gestured to Alice to be silent, and heard a sound from the tunnel. The padding of a large dog.

I tucked the piece of staff with the blade back into my belt. Next I eased Mam’s silver chain from my jacket pocket and coiled it round my left hand and wrist, ready for throwing. With my other hand I picked up the candle, and without further delay I set off after the Bane.

‘No, Tom, no! Leave it be!’ Alice called out from behind. ‘It’s over. You can go back to Chipenden!’

She ran towards me but I pushed her back hard. She staggered and almost fell. When she moved towards me again, I lifted my left hand so that she could see the silver chain.

‘Keep back! You belong to the Bane now. Keep your distance or I’ll bind you too!’

The Bane had fed for the final time and now nothing she said could be trusted. It would have to be dead before she’d be free.

I turned my back on her and moved away quickly. Ahead of me I could hear the Bane; behind me the click-click of Alice’s pointy shoes as she followed me into the tunnel. Suddenly the padding ahead stopped.

Had the Bane simply vanished and gone to another part of the catacombs? I stopped and listened before moving forward more cautiously. It was then that I saw something ahead. Something on the floor of the tunnel. I halted close to it and my stomach heaved. I was almost sick on the spot.

Brother Peter lay on his back. He’d been pressed. His head was still intact; the wide-open, staring eyes showed the terror he had obviously felt at the time of his death. But from the neck downwards his body had been flattened against the stones.

The sight horrified me. During my first few months as an apprentice I’d seen many terrible things and been close to death and the dead more times than I cared to remember. But this was the first time I’d seen the death of someone I cared about – and such a horrible death.

I stood, distracted by the sight of Brother Peter, and the Bane chose that moment to come loping out of the darkness towards me. For a moment it halted and stared at me, the green slits of its eyes glowing in the gloom. Its heavy, muscular body was covered in coarse black hair and its jaws were wide revealing the rows of sharp yellow teeth. Something was dripping from that long tongue which lolled forwards, beyond the gaping jaws. Instead of saliva, it was blood!