Drennan pointed at a small hole in the side of the building, only about five feet high, the place where, once, supplies had been brought in. It was a dark, forbidding place, only just higher than our heads as we sat in the boat. The rower obediently dipped his oars into the water once more and propelled us towards it.

The ceiling of the corridor which ran along the left side of the house was dank and slimy, and the darkness was total until our eyes adjusted. But we soon enough made out a little landing stage, over to the right. Beyond it there seemed to be the faintest outline of a door. We slipped and stumbled our way out of the boat, and onto the slimy stone, Drennan in the lead and me following. He got to the door first and fumbled for a latch. A clunking, scratching sound told me he'd found it. Then I heard him grunt, and the crack of old wood as he put his shoulder against the door and pushed.

A splinter of light. Dark by normal standards, but almost blinding to our eyes. And a great relief as well. We were in. Drennan led the way through, and I came after him, bumping into his back when he stopped to listen. It was all completely quiet. Not a sound could be heard, not even the water lapping against the landing behind us.

'Cort!' I shouted. 'Macintyre? Where are you?'

No reply. Drennan started moving again, his feet on the stone floor making no noise at all, and I became preoccupied with the loud clatter of my boots as I followed. Drennan seemed to know what he was doing; he walked a few steps, then stopped, his head cocked, to listen. Then he walked a few more. After one longer pause, he turned to me and pointed. We crept quietly up a short stone staircase, into a huge room, which must have been about the same size as the great reception rooms on the floors above. There we came across a terrible sight.

Macintyre was lying on the ground, one arm above his head, blood trickling from a wound in the back of his skull. Not serious, perhaps; there was not much blood, but the blow had been enough to knock him unconscious. Cort was sitting on a rickety wooden chair beside him, a flame in one hand, chin resting on the other. In between was a column of masonry reaching perhaps fifteen feet into the air. And around it were half a dozen packages, with a long string coming out of the side, curled round into neat circles and lying on the floor.

'Cort,' I called. 'What the hell is going on here?'

He turned and looked at me. 'Ah, Stone,' he said in an entirely normal voice. 'About time too. I've been waiting for you.'

'What are you doing?'

He said nothing.

'What happened to Macintyre?'

'He tried to take over. Said I didn't know what I was doing. I've had enough of his patronising attitudes.'

'Will you come outside? I think we should have a talk.'

'I've nothing to say to you, Stone. I never want to talk to you again. I know what's been going on. Louise told me. How could you? How could you do that to such a sweet, kind woman?'

'Do what?'

'I know everything. You thought she'd be too ashamed to tell me. And she was, almost; she was in tears, crying her eyes out as she told me what you'd done to her.'

'What are you talking about?'

'She showed me the bruises, the marks of the rope. Everything. Told me what you'd done to her. I should kill you for it. You're a monster. A beast even to think of doing something like that to a woman . . .'

'She's been telling you lies . . .'

'She said you would say that. But she told me about you, Stone. How you attacked her, raped her. The poor defenceless, sweet woman! And it's all my fault! If only I hadn't brought her here, been able to give her the sort of life she wanted. But it will be all right. I'll look after her now. I love her so much. From the moment I saw her, I loved her. I must look after her.'

'Cort, don't be absurd,' I said. 'This is nonsense. She told me the same things about you. She's a liar, Cort. She says these things.'

'Oh, Mr Drennan!' Cort said, frighteningly conversational again. Drennan had been moving softly around the column as I talked. 'Please stand where I can see you. Otherwise I will put this match into the gunpowder here. It will only take a moment to ignite it. Would you be so kind as to stand next to Mr Stone?'

Drennan did as he was told.

'Listen, Cort,' I said urgently and as calmly as I could manage. 'It's not true, do you understand? It's not true. She does that to herself. I know she does. I've got proof, back at my rooms. Do you want to see it? No one has been beating her, whipping her, anything. She's been saying things like that for years. It's all invented.'

'Who would invent a thing like that?' he snarled, reverting to his furious, demented state in an instant. 'Are you saying my wife is a liar? Haven't you done enough already?'

'Look at me.'

He did, suddenly, but only briefly, obedient. His eyes were glassy, wide open. And dark, as they had been on the night of the Marchesa's séance.

'Cort, you've taken opium.'

'Of course I haven't.'

'She gives it to you. What did she give you to drink or eat?'

'You're lying. I can always tell when someone is lying. He was lying too,' he said, gesturing at the still immobile Macintyre. 'He said he was only trying to help. "Only trying to help. Only trying to help,"' he said in a high-pitched childish mimicry which bore no resemblance at all to the way Macintyre spoke.

'So you hit him.'

He nodded.

'And these explosives,' I continued, trying to keep his mind focused on the conversation, 'who set those up?'

'Macintyre did. He brought them over a few days ago. Once they're prepared, the rest is quite straightforward; I just added the rest of the boxes, the ones he didn't use. I don't need help. I can do this job on my own. Wait and see.'

'But Cort, you've used all of it. Far too much,' Drennan said in alarm. 'Listen, I know about explosives. There's enough there to blow up half of Venice.'

'No, no. Just enough to bring down that column. Look, I'll show you.'

His face cleared, and he smiled. And he leaned forward and lit the fuse, which began sputtering.

'Macintyre told me the fuse would last for about ninety seconds. Don't come any closer, mind. I can still set off the whole thing. I'll stay here to make sure it doesn't go out. Don't worry. I'll be quite safe. Macintyre will help.'

'I'm not going without Macintyre. And you,' Drennan said. I could hear that even he was now very worried.

'No.' Cort moved nearer to the explosives, the flame now perilously close.

'What's the point of you killing yourself? How can you look after her if you die as well?'

'I'll be fine. Don't worry about me. I know what I'm doing. Then I'll take care of Stone.'

I looked at Drennan. I didn't know what to do; I rather hoped he did. He'd been a soldier, hadn't he? I could see him looking carefully, his eyes darting from Cort to Macintyre, to the explosives. Back again. Measuring, calculating. And I could see that he was giving up. We were about four yards away; too far a distance to grab Cort and bring him to the ground before he saw what we were doing. He only had to move his hand a couple of inches.

'About a minute left, I would guess,' Cort said thoughtfully.

'Let us take Macintyre, just in case.'

'Oh, no. He has to supervise. He insisted on it. He said he wouldn't trust me to pull a cork out of a bottle.'

Drennan took hold of my arm. 'Come on,' he said quietly. 'We have to get out of here.'

'We can't. We have to do something.'

'What do you suggest?'

'Macintyre is going to die.'

'And so is Cort. And we will too unless you start moving.'

I wish I had been more heroic. I wish I could have seen an opportunity to dash forward and grab Cort's arm. I wish I could have thought of something to say to bring Cort to his senses, or at least distract him for a moment and give Drennan a chance. I wish many things now, and that is enough to indicate that I managed none of them. Drennan had to drag me out, not because of my determination to stay, but because I had frozen, could not move. He dragged me to the door – about thirty-five seconds left, then pushed me down the steps. Only when I fell on the slippery floor did I come alive again, and the panic swept over me. I got up, stumbled – I remember it all – and then ran into the darkness, heedless of where I was going. Just following the sound of Drennan's feet.