Dying to Sin

‘Let’s hope so.’

Kessen nodded. ‘Yes, that’s very helpful. As I said, a good piece of work. However, DS Fry, we’ve agreed your energies would be best employed from this point on exploring the missing persons angle. It’s being neglected at the moment.’

‘Missing persons? But, sir, I think I could be more productive pursuing some other lines — ’

‘No, DS Fry, I think I’d prefer you to concentrate on the missing persons check.’

Fry hesitated too long before she responded, and Kessen registered it.

‘Of course, sir.’

Cooper looked across at her, but she refused to meet his eye. Was it just coincidence that he’d been thinking only yesterday about the DCI’s apparent even-handedness? Was that why he’d noticed this little incident? Or was it that Kessen’s attitude had changed since the arrival of a new superintendent over his head?

Cooper didn’t know how to interpret what he’d witnessed, but he was sure that Diane would be filing the incident away in that very efficient mental filing cabinet she carried around inside her head. He pictured it as the equivalent of one of those old-fashioned green cabinets, heavy and fire-proof, with drawers that slid out on strong, steel hinges.

For a moment, he wondered what was written in his own file — the one pushed to the back of the bottom drawer, slightly dog-eared and crushed out of shape by the more important information in front of it. Nothing he’d want to read about himself, probably.

18

‘SOCOs collected a lot of samples from the kitchen at the farm,’ said Hitchens, assembling the team when the DCI had left. ‘Some old blood traces that the lab is working on, and lots of other stuff, the kind that you might expect in a kitchen. But analysis also found substantial traces of a chemical compound, KNO₃. Potassium nitrate.’

‘Potassium nitrate?’ asked Fry. ‘What is that used for?’

‘The lab thought we might want to know that. Killing tree stumps, for a start. You can get it in most garden centres, or hardware shops. It’s an ingredient of some fertilizers. Also toothpastes that are formulated for sensitive teeth. And gunpowder.’

‘Versatile stuff, then.’

‘Wait — you haven’t heard the best one. Potassium nitrate was considered for many years to be an anaphrodisiac.’

‘A what?’

‘They thought it suppressed sexual desire. It was added to food in all-male institutions. Did you ever see One Flew Over the Cuckoo’s Nest?’

‘The film with Jack Nicholson?’

‘Right. Well, in the film, Nicholson’s character mentions that’s he’s afraid of being “slipped” potassium nitrate in the mental institution where he’s committed. It was a common practice at the time, a way of controlling the behaviour of patients.’

‘Cool. But I’m not sure it helps us.’

‘Is potassium nitrate a natural product, or artificially manufactured?’ asked Cooper.

‘It’s a naturally occurring mineral,’ explained Hitchens. ‘Traditionally, the major sources were the deposits crystallizing on cave walls, or the drainings from dung heaps. Ammonia from the decomposition of urea — you know.’

‘We get the picture,’ said Fry.

‘But it can also be manufactured. The old method was to mix manure, wood ash, earth and organic materials such as straw.’

Cooper nodded. ‘A compost heap, in fact.’

‘Exactly. But they were known as nitre beds, which sounds nicer, I suppose. A heap was kept moist with urine in the, er … traditional manner, and turned to accelerate decomposition. After a year, it was leached with water, and the resulting liquid was rich with nitrates, which could then be converted to potassium nitrate, crystallized and used in gunpowder.’

‘Potassium nitrate is an explosive, then?’ said Fry.`

‘Not on its own. It does have another useful property, though, particularly for fireworks manufacturers. A mixture of potassium nitrate and sugar produces a smoke cloud six hundred times its own volume. Just great for smoke bombs.’

‘How does it kill tree stumps?’

‘It doesn’t really kill them. You have to kill the stump first — then the potassium nitrate makes it decompose faster.’

‘Wait a minute,’ said Cooper. ‘Those compost heaps — did you say they were called “nitre beds”?’

‘That’s right. One of the common non-scientific names for potassium nitrate is — ’

‘- saltpetre?’

‘Correct.’

Cooper found that he wasn’t in the least surprised. It seemed to fit so naturally with what he’d learned already of the owners of Pity Wood Farm, and the other residents of Rakedale.

‘Potassium nitrate is used in Edgar Allan Poe’s story “The Cask of Amontillado” as the lining of the crypt where Montresor buries Fortunato alive. It’s why he has so much trouble with his breathing in his last moments. “For the love of God, Montresor!”’

‘Didn’t the IRA use saltpetre in their bomb-making operations at one time?’ said Fry. ‘I had a feeling it had been put on a restricted list, not available for sale to the general public.’

Hitchens laughed. ‘You can make bombs from sugar and fertilizer, so why would anyone worry about saltpetre?’

‘Also, it’s been implicated in having carcinogenic properties.’

‘I don’t think anyone was worrying about getting cancer or making bombs,’ said Cooper.

‘Oh?’

‘This other stuff in the kitchen. Did it include sesame seeds, by any chance?’

‘Yes, it did,’ said Hitchens. ‘How on earth did you know that, Ben?’

He’d have to ask Amy for the exact wording, but Cooper thought he could remember the recipe pretty well.

Squeeze out the blood. Embalm it in a shroud and steep it in a solution of saltpetre, salt and pepper for two weeks, then dry in the sun. The candles are made from a hanged man’s fat, wax and Lapland sesame.

‘I’d like to make a prediction,’ he said. ‘I predict that if we find another body at Pity Wood Farm, it will be missing a hand.’

Within a few minutes, and thanks to the internet, Cooper knew how to make potassium nitrate himself. The practical part was simple. You could either dissolve solid fertilizer in boiling water, or boil down a liquid fertilizer until crystals started to form. When the solution had cooled to room temperature, it was placed in a fridge. The white crystalline precipitate was mainly KNO₃. Garden products tended to contain ammonium nitrate, too, which contaminated the KNO₃.

‘We should have picked this up earlier,’ said Hitchens. ‘Potassium nitrate can cause eye and skin irritations. Breathing it in can irritate the nose and throat, causing sneezing and coughing. High levels can interfere with the ability of the blood to carry oxygen, causing headaches, fatigue, dizziness and a blue colour to the skin and lips. Even higher levels can cause trouble breathing, collapse and death. Long term, potassium nitrate may affect the kidneys and cause anaemia. Chronic long-term health effects can occur some time after exposure and can last for months or years.’

‘Is this really something you ought to keep in your fridge?’ asked Murfin.

‘No, Gavin.’