As it was, Innocent got up when it was still dark, just. I don’t know how he judged it so well, but by the time we’d bustled ourselves ready the first bluish hint of morning was filtering down to us. I was famished and parched and my feet were sore in my boots when we set off downhill in search of the river. Innocent explained as we walked that countless streams and rivers criss-cross the jungle, thousands of strands of water weaving into tributaries that eventually knit into the mighty Congo itself. We would pick one up nearby, drink, and follow it north; apparently this stream cut quite close to our base camp in the end. He was trying to take our minds off the pain of getting going again, I know. I did the same by imagining the statistics – rainfall measurements, humidity levels, that sort of thing – Amelia would no doubt have contributed if she’d been with us. I hoped she and the others had made it back to camp OK and slept better than us.

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.