There was a ragged split in the wet cover which was old and partly perished. Alleyn displayed the inside. It was stained round the split and not with rainwater. He pointed a long finger. ‘That’s one of her hairs,’ he said. ‘There was a piece of rock in the pool. I fished it out and left it on the ledge. It looked as if it hadn’t been there long and I think you’ll find it fits.’

He fetched it and put it down by the body. ‘Any visual traces have been washed away,’ he said. ‘You’ll want to keep these exhibits intact, won’t you?’

‘You bet I will,’ said Coombe.

There was a sound of footsteps and a metallic rattle. They turned and saw Dr Maine letting himself in at the turnstile. Coombe went down to meet him.

‘What’s it all about?’ he asked. ‘ ‘Morning, Coombe.’

‘See for yourself, Doctor.’

They joined Alleyn who was introduced. ‘Mr Alleyn made the discovery,’ said Coombe and added: ‘Rather a coincidence.’

Dr Maine, looking startled, said: ‘Very much so.’

Alleyn said: ‘I’m on a visit. Quite unofficial. Coombe’s your man.’

‘I wondered if you’d been produced out of a hat,’ said Dr Maine. He looked towards the Spring. The umbrella, still open, masked the upper part of the body. ‘Good God!’ he ejaculated. ‘So it has happened after all!’

Coombe caught Alleyn’s eye and said nothing. He moved quickly to the body and exposed the face. Dr Maine stood stock-still. ‘Cost!’ he said. ‘Old Cost! Never!’

‘That’s right, Doctor.’

Dr Maine wasted no more words. He made his examination. Miss Cost’s eyes were half-open and so was her mouth. There were flecks of foam about the lips and the tongue was clenched between the teeth. Alleyn had never become completely accustomed to murder. This grotesque shell, seconds before its destruction, had been the proper and appropriate expression of a living woman. Whether here, singly, or multiplied to the monstrous litter of a battlefield, or strewn idiotically about the wake of a nuclear explosion, or dangling with a white cap over a cyanosed, tongue-protruding mask; the destruction of one human being by another was the unique offence. It was the final outrage.

Dr Maine lowered the stiffened body on its back. He looked up at Alleyn. ‘Where was she?’

‘Face down and half-submerged. I got her out in case there was a chance but obviously there was none.’

‘Any sign of rigor?’

‘Yes.’

‘It’s well on its way now,’ said Dr Maine.

‘There’s the back of the head, Doctor,’ said Coombe. ‘There’s that too.’

Dr Maine turned the body and looked closely at the head. ‘Where’s the instrument?’ he said. ‘Found it?’

Alleyn said: ‘I think so.’

Dr Maine glanced at him. ‘May I see it?’