'Now, wait,' Doone said. 'The boat can wait. Mr Kendall, you came through the hole, found Mr Goodhaven and brought him to the surface. You sat him on the dock, then dived out under the curtain and climbed onto the bank. Is that right?'

'Yes, except that while I was pulling Harry along to that far corner to give him better support, someone opened the main door above our heads, like I told you, and then went away without saying anything, and I heard a car drive off, which might have been Harry's.'

'Did you hear any car arriving?' Doone asked.

'No.'

'Why didn't you call out for help?'

'Harry had been enticed here- It all felt like a trap. People who set traps come back to see what they've caught.'

Doone gave me another of his a.s.sessments.

Sam said, frowning, 'You can't have dived out under the curtain, it goes right down to the river bed.'

'I sort of slithered under it.'

'You took a sodding risk.'

'So do you,' I said equably, 'most days of the week. And I didn't have much choice. If I hadn't found a way out we'd both eventually have died of cold or drowning, or both. Certainly by now. Most likely Wednesday night.'

After a short thoughtful silence Doone said, 'You're out on the bank. What next?'

'I saw the car had gone. I went to collect my boots and jacket, but they'd gone too. I called to Harry to rea.s.sure him, then I went over to that big shed to find a telephone, but I couldn't.'

Sam shook his head. 'There isn't one. When I'm here I use the portable phone from my car.'

'I couldn't find any decent tools, either.'

Sam smiled. 'I hide them.'

'So I used a rusty tyre lever and a mallet, and I'm sorry about your woodwork.'

Sam shrugged.

'Then what?' Doone asked.

'Then I got Harry out here and put him in a dinghy and we- er- floated down to the lock.'

'My sodding dinghy!' Sam exclaimed, looking at the imitation sc.r.a.pyard. 'It's gone!'

'I'm sure it's safe down at the lock,' I said. 'I told the lock-keeper it was yours. He said he'd look after it.'

'It'll sink,' Sam said. 'It leaks.'

'It's out on the bank.'

'You'll never make a writer,' he said.

'Why not?'

'Too sodding sensible.'

He read my amus.e.m.e.nt and gave me a twisted grin.

I said, 'What happens to the rubbish lying in the dock when you roll up the curtain?'

'Sodding h.e.l.l!'

'What are you talking about?' Doone asked us. 'The bed of this dock is mud, and it slopes downwards towards the river,' I said. 'When the curtain's rolled up, there's nothing to stop things drifting out by gravity into the river and being moved downstream by the current. Bodies often float to the surface, but you of all people must know that those who drown in the Thames can disappear altogether and are probably taken by undercurrents down through London and out to sea.' Sometimes from my high Chiswick window I'd thought about horrors down below the surface, out of sight. Like hidden motives, running deadly, running deep.

'Everyone in the Thames Valley knows they disappear,' Doone nodded. 'We lose a few holidaymakers every year. Very upsetting.'

'Harry's leg was impaled on something,' I said mildly. 'He was stuck underwater. He'd have been dead in a very few minutes. Next time Sam rolled the curtain up, Harry would have drifted quietly out of here, I should think, and no one would ever have known he'd been here. If his body were found anywhere downstream, well then, it could be suicide. If it wasn't found, then he'd escaped justice.' I paused, and asked Sam directly, 'How soon would you have rolled up the curtain?'

He answered at once, 'Whenever I'd found the hole in the floor. I'd have gone to take a look from beneath. Like we're going to now. But I hardly ever come over here. Only in summer.' He gave Doone a sly look. 'In the summer I bring a mattress.'

'And Angela Brickell?' Doone asked.

Sam, silenced, stood with his mouth open. A bull's-eye, I thought, for the Detective Chief Inspector.

I asked Sam, 'What's under the water in the dock?'

'Huh?'

'What did Harry get stuck on?'

He brought his mind back from Angela Brickell and said vaguely, 'Haven't a clue.'

'If you raise the curtain,' I said, 'we may never know.'

'Ah,' Doone stared judiciously at Sam, all three of us still cl.u.s.tered round the open door. 'It's a matter for grappling irons, then. Can we get a light inside there?'

'The main switch for here is over in the shed,' Sam said as if automatically, his mind's attention elsewhere. 'There's nothing in the dock except maybe a couple of beer cans and a radio some clumsy bimbo dropped when she was teetering out of a punt in high heels. I ask you-'

'Harry wasn't impaled on a radio,' I said.

Sam turned away abruptly and walked along the path to his workshop. Doone made as if to go after him, then stopped indecisively and came back.

'This could have been an accident, sir,' he said uneasily.

I nodded. 'A good trap never looks like one.'

'Are you quoting someone?'

'Yes. Me. I've written a good deal about traps. How to set them. How to catch game. The books are lying about all over the place in Sh.e.l.lerton. Everyone's dipped into them. Follow the instructions and kill your man.'

'You're not joking by any chance, are you, sir?'