Marius just nodded wearily and dozed. He woke to find the army had moved forward ten kilometres in the last day. ‘We are driving them to the sea,’ a wounded soldier with a torn shoulder said. ‘I saw the British running away from us. Running. The war will be over in a week.’

But by the end of the day the soldier was grumbling about his hunger. ‘The supply wagons can’t keep up with us,’ Doctor Weger told him. ‘The British are running too fast.’

The wounded soldier spat on the ground. ‘The generals don’t care about our bellies.’

The doctor pushed his spectacles back on to his nose. ‘And the medicines we need can’t keep up with us either,’ he told the soldier. ‘We have so many fever cases. More men are falling sick with flu than from bullets.’

‘I have a cure for the fever,’ Marius said quietly. ‘My grandmother taught me.’

The doctor looked at him. ‘Witchcraft was it? Eye of newt and toe of frog stuff?’

‘No, she made it from the bark of a willow tree.’

The doctor nodded slowly. ‘Yes. Willow tree bark. Our German chemists have been making it for twenty years now. They call it Aspirin. We don’t have any.’

‘But we’re near the River Somme,’ Marius said. ‘I’ve seen willow trees on the banks. I can make willow tea from the bark.’

Again Doctor Weger nodded. ‘The men in the fever tent are dying. We have nothing to lose, young man. I’ll send a couple of fit men to help you collect the bark. But hurry. We’ll be moving on again tonight.’

And so Marius’s new life began. Each day he gathered the willow bark and stewed it to make his fever cure. Some men were cured and some were as ill as ever. But Marius had moved on ever westwards before he saw them killed or cured.

The soldiers who came to the hospital tents were exhausted now. They weren’t singing songs about driving the British back any longer. They were complaining of tiredness and hunger and always that fever, which was striking down their friends. Every night they moved west. Every night they moved less than the night before.

As the sun rose on Tuesday 26th March Doctor Weger took Marius with him through the woods so they could be closer to the fighting than the boy had ever been. They stood at the edge of the trees, high on a ridge above the River Somme, and looked down on the war below.

The air was filled with sounds like whistles or screams. Fountains of earth leaped towards the sky as shells exploded overhead like inky-black flowers. The ground shook and between the explosions there was the droning of aeroplanes battling across the morning sky. White clouds of steam hurried across the valley. Great oak trees lay shattered where the armies had battled through.