He and Fox moved to where the roof had originally overhung the excavation. Here they looked down on the whole subsidence. Tiny runnels of friable soil trickled and started at their footfall. They found no footprints or traces of obliteration.

Alleyn said: ‘I think you’d better take over here, Br’er Fox, if you will. Meet the doctor when he comes and when he’s finished bring him down to the lock.’

As he went down the hill Thompson’s flashlamp blinked and blinked again.

The River was still misted but when Alleyn looked into the lock, there was the roof of the Zodiac’s wheelhouse, her deck and the tarpaulin cover, the top of a helmet, shoulders, a stomach and a pair of regulation boots.

Light from the saloon shone on the wet walls of the lock. He could hear voices.

‘Hallo,’ he said. The constable looked up and saluted. He was the man who had been on duty by the pub.

‘There’s a ladder at the lockhouse, sir,’ he said.

‘I’ll drop, thank you.’

He managed this feat and for what turned out to be the last time, met the Zodiac passengers in the Zodiac saloon.

IV

They were in what Fox liked to call déshabillé and looking none the better for it with the exception of Dr Natouche who wore a dressing-gown of sombre grandeur, scarlet kid slippers and a scarf that bore witness as did none of his other garments, to an exotic taste for colour. He was, indeed, himself an exotic, sitting apart at a corner table, upright, black and without expression. Troy would have liked to paint him, Alleyn thought, as he was now. What a pity she couldn’t.

The Skipper also sat apart, looking watchful. Mr Tillottson was back at his former table and the passengers were in the semi-circular seat under the windows. Hewson at once began a heated protest. His sister! Where was his sister! What was the meaning of all this! Did Alleyn realize that he and his sister were American citizens and as such were entitled to protest to their Ambassador in London? Did he appreciate—

Alleyn let it run for a minute and then clamped down.

‘I think,’ he said, ‘that we do have a rough idea of the situation, Mr Hewson. We’re in touch with the Federal Bureau in New York. They’ve been very helpful.’

Hewson changed colour, opened his mouth and shut it again.

Alleyn said: ‘Do you really not know where your sister has gone?’

‘I know,’ he said, ‘she’s been real scared by you guys acting like you thought—’ he stopped, got to his feet and looked from Tillottson to Alleyn. ‘Say, what is all this?’ he said. ‘What’s with you guys? What’s happened to Sis?’ He fumbled with his hearing-aid and thrust his deaf ear towards Alleyn. ‘C’mon,’ he said. ‘C’mon. Give, can’t you?’