We reached the river soon enough. It was more of a stream really, not more than ten feet wide. The ground either side of it was boggy, stabbed full of reeds, and the water itself was brown as tea, but I was so thirsty I didn’t care. Scrabbling for my empty water bottle, I started to wade in. Innocent stopped me.

‘We need to purify it first.’

The thought of waiting while we built a fire – out of what, damp sticks? – and boiled water – in what? we hadn’t brought a pan – to purify it nearly made me snap, but he smilingly held up a hand, rooted in his pack, and produced a little plastic tube.

‘Clever tablets,’ he said.

Clever, but slow: once added to our refilled water bottles the tablets took thirty agonising minutes to work, and that half an hour waiting for the water to be safe to drink was an eternity. Being as parched as that made me realise I’d never actually experienced proper thirst before. Even when I’d thought I was thirsty after sport, say, I wasn’t really: my entire life, when I’ve wanted water to drink, I’ve been able to turn on a tap within minutes. I’d only gone, what, twelve hours without a drink now, but I’d been sweating in the humidity and the thirst I battled as I sat waiting for that tablet to work tasted like ash and headaches, sawdust and scabs. Innocent himself seemed perfectly content to wait, but I could tell Caleb was hurting too. Though he didn’t say so, I saw him looking at his watch and he caught me looking at mine. Perversely, when the thirty minutes were up, I held back from taking the top off my bottle. So did Caleb. Innocent took a sip from his own flask but we both waited. I didn’t fully understand why to begin with, though it was perfectly obvious. Neither of us wanted to crack first. As soon as I spelled that stupidity out to myself I said, ‘Ridiculous,’ unscrewed the lid, and drank half the bottle in one go. I’m pretty sure I caught Caleb smiling before he followed suit.

Purification tablets make water taste of chlorine, like a swimming pool, and there was grit in my bottle, and the water was lukewarm, but just as Innocent’s boiled sweet had been the best I’d ever eaten, that was the most welcome drink of my life. Everything – even my sore feet – felt better after it. The water evidently rebooted Caleb too. ‘Come on then, we should make tracks,’ he said, bouncing on the balls of his feet. This show of readiness was unnecessary as Innocent and I were already primed to go. But Caleb obviously wanted to assert that he was in charge, so not content with having chivvied us pointlessly, he set off into the jungle, swinging his machete this way and that, a self-appointed expedition leader.

The only trouble was that he’d started out in the wrong direction again. It’s hard to navigate in the jungle, I know, but we were supposed to follow the stream north, meaning the morning sun would be coming from our right, and Caleb had set off with the sun to our left. After he’d taken a few steps I glanced at Innocent, first to make sure I hadn’t gone mad, and second because I didn’t want to be the one to correct him. I’m pretty sure Innocent shot me a smile.