‘You say that no one would have suspected potassium nitrate poisoning,’ said Cooper. ‘But his brother Raymond might have suspected it, if he knew what Derek was up to.’

Hitchens shook his head. ‘That old man? How would he have known the effects of potassium nitrate? Who knows what saltpetre is exactly? I didn’t, until just now.’

‘Even so, he must have wondered what was wrong. You don’t just drop suddenly without any other symptoms, do you?’

Hitchens checked the report. ‘Eye and skin irritations, sneezing and coughing, headaches, fatigue, dizziness, a blue colour to the skin and lips, trouble breathing.’

‘I found several sites on the internet where I could order food-grade saltpetre. Lots more where it’s listed as an ingredient in garden chemicals.’

‘OK.’

He’d also found a method for treating skin infections that had supposedly been passed from father to son over many generations in farming. If you got bitten or scratched and it looked as though the wound was getting infected, you should bathe the area in a solution of hot water and saltpetre. It inhibited the growth of organisms associated with skin infections. Clostridium, Streptococcus and Staphylococcus. It made sense. He was just surprised that he’d never heard of it in his own family. Father to son over generations? Maybe Matt used the treatment on the quiet.

‘Ben – this thing about a hand of glory,’ said Fry, interrupting his reading. ‘You don’t think you’re letting the superstition business get to you too much?’

‘Not me. I think it had got to Derek Sutton, though.’

‘You really think there’s a body without a hand somewhere?’

‘Yes.’

‘Prepared to bet on it?’

‘I’m not really a betting man,’ said Cooper.

‘Ha-ha.’

Potassium nitrate had a smell reminiscent of burnt gunpowder. That rang a bell with Cooper. For a while, supplies of fertilizer had been stored in a breeze-block extension to the main barn at Bridge End. The inside always had a heavy smell of potassium nitrate fertilizer. Burnt gunpowder was right – it had always made him think of Bonfire Night and firework displays.

He would probably never be able to go to a garden centre without being reminded of it these days. Not without being reminded of poor Derek Sutton, preparing his saltpetre recipe in the kitchen at Pity Wood.

Fry was seething quietly at her desk when Hitchens appeared at her side, his face creased with discomfort.

‘Diane, have you got a minute?’

‘Sir?’ said Fry, automatically responding to the tone of his voice. It was a management tone, the kind of voice people used when you were being summoned into their office for a reprimand. Or to get bad news. ‘Is something wrong?’

‘Let’s just step into my office, shall we?’

They moved out of earshot of the team in the CID room and Hitchens shut the door of his office with a deliberate slam.