Mackenzie remembered that season of his life all too well. Ice was like coffee with the volume turned up to a thousand. It was a euphoric lava flow just beneath your skin. It could keep you awake for days, and the brain is just not meant to be awake for that long. The body needs sleep more than it needs food.

‘Ready, set, go,’ said Shelby with a huff of air.

She crushed up a whole box of Sudafed pills with a mortar and pestle, then tipped them into a glass beaker. She poured in a solvent from a marked bottle. ‘You’ve got to separate out the pseudoephedrine,’ she said. ‘We mix it with a solvent at low temperatures to remove it.’

She began setting up other vials, beakers, a Bunsen burner.

‘Once the pseudoephedrine has been distilled and it’s risen to the top of the solvent, it’ll be oil, and then we’ll burn it off with this: a reflux condenser. The steam runs up, gets cooled, then drips down here.’ She traced the path with her finger through the glass tubes.

Mackenzie had seen part of this process before, but with different chemicals. There were a hundred different ways to cook ice. He’d never seen it done this way, but he made it a habit not to watch the product being made. If people thought you knew how to cook, you became one of two things: a god or a slave.

But in Shelby’s case, he’d let her explain it to him. It seemed to help her work, and he didn’t want her feeling alone as she stepped into something so major.

‘After it turns into liquid,’ Shelby pointed to where the steam was condensing, ‘you run red phosphorous and hydrochloric acid through it. That’s where you have to get the pH level right. This is where ninety per cent of people muck it up. If the pH is way too high, it’ll just burn. But even if it’s just a little too low or too high, it’ll hurt your body.’

Mackenzie peered closer at the red phosphorous. ‘Where did you get this? I thought you couldn’t buy this stuff.’

‘Get too close and you’ll be sorry,’ she warned. ‘No, you can’t buy it. It’s illegal to have red phosphorus without a good reason. So you can spend weeks scraping it off matches . . . or you can have friends who work in the chemistry department at the university.’

‘Shelby, you can’t do that! You’ll lead them straight to us! Police monitor chemicals like this!’

‘I’m going to make it as safe as possible, and we’re not doing this long-term, right? So we’ll be fine.’ She stepped away from her work. ‘Damn it, Mackerel, now I’m shaking.’

‘Don’t call me Mackerel,’ he said. ‘My name is Mackenzie.’