The River Somme sat like a muddy, abandoned ribbon in the valley below them to their right. The roads along its banks were filled with motor-lorries and carts pulled by weary horses. They all struggled across the potholes left by years of battles. Men tried to keep the ruts repaired with gravel but the traffic soon gouged great grooves again.

The woods were little more than splintered trees. An orchard had escaped the shells but the enemy had flattened it as they fled east so the British could not enjoy the late summer fruits.

The young travellers rested and looked from their high ridge across the broken land. The fields were littered with cemeteries and old trenches, shattered villages and deserted concrete shelters that the Germans had left a week before.

A raging storm of fire and steel had passed over the land and left a grey-green-brown patchwork desert.

All the farm animals had gone and rats made the trenches their homes. The girl and boy hadn’t spoken much but now the light was fading. ‘I’d thought we could shelter in one of the dugouts... but they don’t look very healthy,’ Aimee said.

They’d reached the line where the British had been a few months ago, before the Germans drove them west. Aimee climbed down a rotting wooden ladder to the floor of a trench. Mouldering boards covered the dark green stinking slime of the mud at the bottom. A light rain began to fall and turned the planks slippery.

Aimee helped Marius down the ladder and a rung snapped. He fell backwards and lay numb for a minute. He was breathing heavily. Then he struggled to his feet, where he swayed, giddy and sick.

‘We can’t go on much more today,’ said Aimee. ‘Let’s see if there’s a dry dugout we can rest in.’

The dugouts were cut into the sides of the trenches and smelled even worse than the trenches. They were overgrown with purple weeds. Aimee pulled a gas-curtain aside and ducked into the darkness. ‘Pass me the matches,’ she said to Marius. He found them in the pack and lit a candle inside a lantern.

The amber light showed a rough table with papers still scattered over it. The British had left in a hurry.

The earth floor was damp but there were bunk beds made of solid timber and steel plate raised up and dry. They had once had blankets but the rats had chewed them to shreds. A soldier had left a magazine and Aimee read a scrap of a poem. It was one of the comical newspapers that the British wrote themselves.

Aimee frowned as she read it. ‘What is it?’ Marius asked.

It’s a poem,’ she said. ‘A poem called “The Little Soldiers of the Night”.’

‘Soldiers of the night?’

‘It’s not about soldiers... it’s about the lice that crawl over their bodies... you see?’

‘No.’