‘That’s a good sign,’ said Amelia in my ear.

‘Why?’

‘Chimpanzees eat colobus monkeys.’

I know Amelia well. She was pointing out a fact, not hoping to see the beautiful creatures above us torn apart.

Xander, however, looked worried. ‘And that’s a good thing?’ he said.

Caleb answered for Amelia. ‘Means they might be close. If we’re lucky we could even get to see them hunting, I suppose.’

Happily – on all counts – Innocent corrected him. ‘That’s unlikely,’ he pointed out gently. ‘If there were chimps nearby, the colobus wouldn’t be so relaxed.’

13.

We pushed on further into the jungle, with Innocent telling us the names of the plants and trees. They mostly went in one ear and out the other, if I’m honest, but the most common plant we had to hack through at ground level was a straggly thing about my height, with longish blue-green leaves. Innocent told us the pigment in those leaves was hypersensitive to light, little of which managed to filter through the canopy above.

Though I don’t know what those straggly plants were called I do know the name of the bird responsible for the ‘ka-ka-ka’ noise that erupted close by while Innocent was telling us about the pigment. The kaka bird. Obviously. Later he pointed out an aardvark hole, twice the size of the entrance to the badgers’ set on the north slope of Pitch Hill back home in the south of England, and later still he stopped beside an enormous mound, the surface of which was alive with termites, shimmering in the gloom like petrol on tarmac.

The heat pressed in from all sides.

My shirt stuck to my back, my trousers stuck to my legs, my boots stuck to my feet.

We walked for hours.

We didn’t see any chimpanzees.

But just as I was about to give up hope and suggest we head back to camp and try again the following day (somebody had to crack; I wasn’t too proud to do it) Marcel, who was leading the way, stopped dead mid-machete-swing. We all paused. I heard Amelia beside me take in a breath to ask what was going on, and held up my own hand to shush her, just in time. We all stood still.

‘Bingo,’ sang Innocent.

All at once there was a mighty eruption of shriek-chattering and the canopy ahead of us shook as the troop of chimpanzees we’d walked all this way to see dropped and climbed and swung, hand over hand over hand, from branch to vine to branch, some lowering themselves all the way down to the patchy undergrowth, others ricocheting up into the treetops. Innocent motioned for us to squat down next to him and gave us each a blue paper hospital mask. As I fiddled to put mine on he explained that this troop, led by an alpha male called Bingo, were habituated to humans. The cacophonous display was a greeting of sorts. But although they were used to people, and therefore would tolerate us getting close, that made them vulnerable to catching any harmful bugs we might be carrying.