‘He has cyanosis, look – the bluish discolouration of the fingers, toes and ears, and around the mouth. That’s caused by a dramatic drop in the oxygen content of the blood circulating through the body. Blood poor in oxygen is purple, rather than red.’

‘But he was found in a flooded bunker,’ said Fry. ‘I assumed . . .’

Mrs van Doon shook her head. ‘If this bunker of yours regularly gets wet and dries out again, I imagine there was a certain amount of rusted metal around.’

‘Yes, there was.’

The pathologist hadn’t even picked up on her slip, her use of the word ‘assumed’.

Never assume, it makes an ass . . .

‘Oxidized metal produces carbon dioxide, and that’s lethal in a confined space,’ said Mrs van Doon. ‘Even without the hatch being closed, the victim was at serious risk. He could have passed out fairly quickly, especially if he was panicking, and exerting himself physically.’

Fry looked at Michael Clay’s blue-tinged fingers. ‘He would have been running up the ladder, trying to force the hatch open. Shouting for help.’

‘Of course. No ventilation either, I suppose?’

‘A couple of sliding vents, but they were rusted shut.’

‘It wouldn’t have made any difference if they’d been open,’ said the pathologist. ‘Carbon dioxide is heavier than air. Without a pump to replenish the atmosphere, he wouldn’t have survived very long. As things went downhill, he would have become confused and disoriented, losing co-ordination. His breathing would have progressively weakened, like a fish out of water, and then he would have lost consciousness. Sometimes, people die from cardiac arrhythmia before the asphyxia.’

‘So he was already dead when the bunker started to flood?’ asked Fry.

‘Mmm.’ Mrs van Doon tapped a scalpel thoughtfully against a stainless-steel dish, a habit that Fry normally found irritating. Today, it didn’t seem to matter. ‘Perhaps not when it started to flood. It would have taken time.’

‘So he would have lived long enough to see the water coming in?’

‘I think so. It’s all a bit academic, perhaps.’

‘I bet it didn’t feel academic to Mr Clay,’ said Fry, trying half-heartedly to get a reaction.

‘Perhaps not.’

‘More like something out of an Edgar Allan Poe story.’

‘Poe?’

‘He was the writer obsessed with premature burial.’

‘I don’t remember that particular story,’ said the pathologist mildly. ‘I was always scared by the one that had the walls gradually closing in. That used to give me serious nightmares.’

Fry shook her head. ‘For me, it’s drowning slowly, as the water gets higher and higher. Trying to get one more gasp of air, but feeling the water reach your mouth. As far as I’m concerned, it would be a blessing to pass out from lack of oxygen first.’

Then the other woman met her eye properly for the first time. Fry felt a physical shock from the contact. Was there sympathy in her expression? Surely not pity? God, please don’t let the pathologist be feeling pity for her.