My father set up our first reconnaissance at Gilgil. The town was small enough to need only a railway siding that connected to the running line in a loop at either end. Another branch had been built in 1929 connecting to Thomson’s Falls, whose cold, clear water drained from the Aberdares and plunged over two hundred feet into a forested ravine.

My father was pacing by the side of the track when I arrived; his face lit up when he saw me, and he waved me over.

‘Good, good,’ he said, pumping my hand enthusiastically. ‘Are you ready to start?’

‘I think so.’

‘Good.’

The track was just over three feet in gauge, and lay flat on the ground at this point in its journey. Elsewhere it was raised, on bridges over rivers and valleys, or sunk, as at Nairobi, but at Gilgil it was possible to walk right up to the rails. When the train was in the station small African children would appear and pass bright green bananas through the open windows in exchange for the passengers’ coins. Even when the train was moving, I’d seen them run alongside, trying to catch the attention of the bwanas and bibis. To the left of the track, the ground sloped away after four or five feet to dense green bush and red and purple hibiscus. Up ahead there was nothing but open land.

We tramped along in silence for a few moments. It was dusty underfoot, and the shins of my father’s trousers were covered in a fine layer of reddish-brown. Eventually he cleared his throat. ‘I didn’t know whether to start here or with Voi. What do you think?’

I looked over my shoulder at the station, a few hundred yards or so behind us. Even from a distance I could see that the paint on the woodwork was peeling, and weeds had sprung up through cracks in the floor.

‘Voi is mile one hundred,’ my father said. He stopped and fanned his face, which was turning puce in the sun. ‘It’s mile four hundred and seven here – doesn’t have quite the same ring.’

‘There’s the marshalling yard at Voi.’

‘And it’s the junction for the feeder to Tanganyika …’

I looked back at the station again, shading my eyes against the glare. A cluster of men had gathered in the shade at the edge of the platform. ‘On the other hand – all the farmers use Gilgil – everyone in the Wanjohi uses it in fact.’

‘Is that so?’

‘It’s one of the main auction towns. And it’s a big area for flax.’

We started walking again, my father clasping his hands behind his back. His expression was thoughtful, and I was pleased – more than pleased, proud – that my opinion mattered to him.

‘What about the new town they built around the station for Thomson’s Falls?’ I said.

‘What of it?’