"Yes. Well, not that exactly, but that kind of thing. "

"Well I don't think that. I'm a little worried that I still don't know what you really look like, but that's more from uncertainty than the idea that you might live in a mushroom. I would like to know what you're really like, but I recognise that it's not my right to know and you'll show me as and when you wish to. I reserve the right to be shocked, inspired or terrified then." It was a bald statement of truth, which I knew she would hear in my words, though it just came out like that. I had wanted to be honest, and now I was worried I had gone too far.

"Oh, Rabbit. You say the nicest things." She stepped forward and kissed my cheek and then walked off down the pavement, leaving me more baffled than ever. I shrugged and followed, turning down a side alley that wound past the Devereux Inn and between the backs of buildings into an open courtyard with a fountain. When I caught up with her, she was standing at an inconspicuous doorway. "Is this it?"

"According to Marshdock there should be a way down through here." She pressed her hand against the flaky paint on the heavy wooden door and pushed. The door swung open and there was a stairway down into darkness.

Blackbird led the way down and I followed. I turned on my torch as the door swung shut with a solid thunk behind us.

It was easier walking down the stairway in the torchlight than in my own flickering glow. It wasn't that the torchlight was better illumination, but it didn't shift and sway of its own accord. We descended a little way then turned back on ourselves, with the sound of water getting stronger as we went down. Another flight down we turned back again and I could clearly hear the water now.

We came out onto a walkway made of bricks that stretched out in either direction into darkness. In front of us was a weir with teeth of rusted metal sticking up out of the water, combing the larger detritus from the flow. It was about fifteen feet wide and the water falling the three feet to the next level almost drowned out our voices.

"Which way?" Blackbird shone her torch up and down the tunnel.

"Upstream, I guess. We want to go back towards where Australia House and the Royal Courts of Justice are."

She set off ahead, her torch swinging around the vaulted ceiling. I had a moment's thought for what would happen if there was a sudden downpour and then went after her.

The narrowness of the walkway meant it was easier to walk near the water, but it was also where the footing was slimier and I constantly found myself having to negotiate past nameless rubbish washed up in the last flood. We made our way slowly upstream, bending around away from the noise of the weir to find another weir in front of us. Bottles and rubbish were caught in the teeth for now, but that would soon change if it rained. I wondered where it washed out and then realised I knew. I had seen the iron grid of the outflow in my vision where it emptied out into the Thames. We curved around again and the noise changed tone. It became deeper and reverberant. The tunnel ended suddenly and I knew where we were. "Here. It's here," I called to her.

The s.p.a.ce opened out into a vaulted cavern. At the far end from us was a waterfall, some eight or ten feet tall with ladders either side providing access to the upper level. There was a metal gantry over the waterfall. The ceiling went up straight fifteen feet or so from there then curved into a vaulted brick roof. I swung my torch around and dropped the beam so I could see the island. It was in the centre of the pool of water fed by the waterfall. Now I could inspect it I could see that it was man-made and brick-sided. The top was shelved with outward sloping layers and in the centre of it I could see what we had come to find.

I didn't need to see it to know it was there. It sang to me in a low discordant hum that set my teeth on edge and made my stomach sour. The anvil sat on its plinth, malevolent and dark, streamers of nameless filth caught on it. Nor did I need to touch it to know what it would do to me if I did.

"It's just like you said," shouted Blackbird over the constant thunder of water, she walked forward level with the island.

"There should be a door in the wall, over there." I swung the torch around across the wall on the other side, finding vaulted alcoves built into the walls. There was a darker outline, rectangular in the wall opposite. I couldn't see it clearly in the torchlight, but I knew it was there. The only way I could see of getting across was to climb the waterfall and then cross the gantry down on to the other side.

"We'll go over at the gantry," I shouted to Blackbird and pointed my torch.

"No need," she shouted back. She took a step or two backward and then skipped forward and launched herself off the walkway ending up on the island, ten feet away, with an easy grace. She edged her way around the plinth with the anvil on it and readied herself to jump across to the far bank. There was no way I was attempting that.

"I'm going the long way around," I shouted over to her. Apart from the difficulty of jumping across, I did not want to get that close to the anvil. I made my way to the gantry ladder. It was stained and smeared with slime, like everything else, but it looked sound enough. I could have done with some protective gloves, but I would just have to settle for washing my hands thoroughly when we got back to the surface.

I put my hand on a rung at chest level and rattled it, making sure it was secure. It held firm, so I tucked my torch in my pocket and put my foot on the rungs and started climbing. I reached the top without incident and hoisted myself up onto the gantry. This was above flood level, so although it wasn't pristine it wasn't smeared with slime like the ladder. I used the handrail to walk across, pulling my torch to take a look at the anvil from this higher viewpoint.

From this new perspective, it was clear what it was. The shape of it, with the horn sticking out at one end, was quite distinctive. It was only the streamers of flotsam and filth that disguised its true nature.

I switched off the torch and replaced it in my pocket so I could have both hands free for the climb down. I could see that Blackbird had leapt nimbly across to the other side and was investigating the wall. I knelt down, reversing towards the ladder and feeling with my feet for the rungs below me.

It was tricky to balance on the edge and move backwards onto the ladder. Concentrating on that, I didn't notice the light growing in the distance down the long tunnel in front of me until I had my hands on the rungs and was climbing down the ladder, about to drop below eye-level.

What caught my attention was not the way the arch of the tunnel was illuminated. It was the way the light flickered, sending shifting milky beams across the domed ceiling as if it was reflecting off the water.

Except it wasn't the water that was causing it to flicker.

Thirteen.

I had to look twice before my brain caught up with my eyes. Then I looked at my hands and, no, it wasn't me creating that shifting luminescence. That meant only one thing.

My scramble down the ladder may have been ungainly and noisy, but the clatter was easily drowned out by the thundering waterfall, which also meant my attempts to attract Blackbird's attention went unheard. I had to make sure that the light from Blackbird's torch did not give us away.

I made it to the bottom and then had to fumble in my pocket for my torch. The ledge was narrow and it was still pitch dark. The torch tangled in my pocket and I wrenched at it to pull it free. My fingers were slimy from the ladder and as it came free it slipped out of my fingers and bounced on the bricks at my feet then skidded over the edge and vanished into the dark water below. I swore.

There was no time to see where it had gone. I used my hands to feel my way along the clammy wall, stepping sideways towards Blackbird. I could see the glimmer now on the tunnel ceiling over the gantry. It was getting stronger.

I shuffled towards the place where Blackbird was examining the wall with her torch. I daren't go any faster for fear of losing my footing. I finally reached her and tugged at her coat. "Blackbird, we have to get out of here!"

"What's the matter? Where's your torch?"

"I dropped it."

"Already?"

"Turn yours off. There's someone coming."

She turned off the torch. "Where did you drop it? "

"Never mind. Look." I pointed upwards to the glow building above the gantry.

"Why didn't you say?" She started shifting along the ledge.

"I was trying to. You were more interested in the torch." The light was growing over the gantry and starting to illuminate the vaulted ceiling.

"There's no time. In here." Blackbird dragged me into one of the alcoves created by the vaulting. The alcove was shallow and we crammed into the limited shadows created by the supporting pillar.

The light grew brighter and then spilled out over the water. I pressed in alongside Blackbird.

I leaned forward. There were two figures standing on the gantry. One of them was a blank silhouette against the dark, a wraithkin like me. I pressed myself in again. "How many?" Blackbird whispered against my chest. "There are two, a wraithkin and one other. The other looks normal enough. "

"Can you see what they're doing?"

I leaned forward again slowly. Blackbird tugged at my sleeve. "Don't let them see you."

"I know. I won't."

I leaned out again to peak around the pillar. The two were still on the gantry with the normal-looking one making grand gestures towards the central island and the anvil. The conversation was quite animated, but we were too far away to overhear them.

"They're arguing."

"What about?"

"I don't know."

"Let me see." She leaned forward across me while I leaned back against the wall.

"They're coming down."

"s.h.i.t! Can we hide?"

"Not with magic. Your first use of it would give us away like a beacon."

"Then let's run for it."

"We'd never make it. If it comes to it, jump into the water and let the flow carry you downstream to the weir. Try and stay underwater for as long as you can."

"I can't swim."