‘First of all, hydrogen peroxide,’ said Fry. ‘That’s basically plain water with an extra oxygen atom, according to the chemist. I didn’t know that.’

‘Hair bleach?’

‘I’m thinking peroxide blondes,’ said Murfin. ‘Jean Harlow, Marilyn Monroe.’

‘Yes, back in the fifties and sixties, that was the popular way to dye your hair at home.’

‘Do people still use it?’ asked Cooper. ‘I heard it turns your hair orange.’

Fry gave him a challenging look. ‘How would I know, Ben?’

‘I’ve no idea. Sorry.’

‘Isn’t it used as a fuel, too?’ suggested Murfin. ‘I think it was leaking hydrogen peroxide that blew up that Russian submarine a few years ago.’

‘The Kursk, yes. How did you know that, Gavin?’

‘I’ve got a teenage lad. He’s interested in things like that, so I get lectured about them at the dinner table.’

‘The chemist’s report says that about half of hydrogen peroxide produced is used to bleach wood pulp or paper, as an alternative to chlorine-based bleaches. He also suggests mouthwash, contact-lens cleaning solutions, and dental-bleaching gels.’

‘More to the point,’ said Cooper, ‘it’s added to animal feed sometimes, to help fibre digestion. And it’s in some fertilizers, too. I think you can even use hydrogen peroxide in septic tank systems. It oxidizes the slime.’

‘Lovely. So no surprise to find it on a farm, then?’

‘What else is there in the report?’ persisted Cooper.

Fry sighed. ‘Dilute hydrochloric acid, also known as muriatic acid. Bricklayers use it to clean mortar off bricks, because the acid dissolves the lime in mortar. It’s used for cleaning concrete, too. It doesn’t take a big leap of the imagination to figure out where that came from. The builders have been at Pity Wood Farm for weeks.’

‘Isn’t hydrochloric acid dangerous?’ said Murfin. ‘It sounds dangerous.’

‘In the concentrated form, yes – you’d get a pretty severe burn without protective gear. But this is a commercial solution, and less dangerous. I’d still wear gloves and a face mask, though, if I were you.’

‘Next?’ asked Cooper.

‘Potassium hydroxide, also known as lye.’

‘Drain cleaner.’

‘Problems with the drains at Pity Wood? I should say so. What about you, Ben?’

‘OK.’

Fry turned to the second page of the report. ‘Iodine tincture.’

Cooper had used that himself many times, spraying it on to the umbilical cords of new-born lambs and calves as a disinfectant. There were always cans of iodine aerosol standing around at home.

Fry looked up for a comment, but got none. She was smiling now, feeling that she’d been proved right. She was on the home stretch if Cooper wasn’t even commenting.

‘Methanol,’ she said. ‘Even I know that’s antifreeze. Everyone has it, if they own a car. I’ve got some myself.’ There was a continued silence, and she pressed on quickly. ‘Last couple now. Propan-2-ol. Isopropyl alcohol. Any takers?’