One was a man in British army uniform. But the other seemed to be a girl in a smock dress and the man was lifting her above the side of the basket. ‘It’s a girl,’ Marius screamed. ‘Don’t shoot.’

Through the roar of the wind and the engine the pilot didn’t seem to hear. Marius reached forward and slapped the man hard on the shoulder just as he took one hand off the controls to press the trigger on the machine gun facing forward.

The plane lurched, the bullets sprayed wide of the grey monster. Hot gusts of air from the gun blew back in Marius’s face. The pilot turned and looked back angrily. ‘You made me miss.’

‘But it’s a girl in there,’ Marius cried.

‘One girl or dozens of our gunners,’ the man shouted in reply. ‘Sit down. I’m going in for a second pass.’

The plane wheeled through the sky and turned back towards its helpless target. The faces of the man and girl had vanished.

This time he wouldn’t miss.

26 March 1918: East of Bray

As Silver Hand held the girl over the side of basket he felt the balloon jerk. The ground crew had seen the German plane before Sergeant Grimm or Aimee had.

‘Albatross J2 from the east,’ an officer barked. ‘Height one thousand feet. Prepare to fire anti-aircraft guns... and get the balloon down as fast as you can.’

‘It won’t be fast enough, Captain,’ a soldier said as he put the cable motor into reverse and started to wind in the cable.

He was right. It was slow, too slow. Still, the sharp downward tug of the cables sent Silver Hand falling backwards into the basket and Aimee fell alongside him. They struggled to their feet and looked at the nose of the aircraft whirring towards them. They looked down the barrels of two machine guns.

The plane swerved a little as the guns spat their fire and the ripple of bullets missed. In a moment the plane had rolled on its side and was turning for a second attack. Aimee watched, helpless, as the enemy came back. The pilot in goggles seemed to be arguing with a small soldier in the back seat whose pale face looked afraid.

Anti-aircraft shells were exploding around the plane as the men on the ground tried to track it and shoot it down. But it was moving too fast.

‘Where are those fighter planes we were promised? The Sopwith Camels?’ the British officer groaned.

Sergeant Grimm had sunk into the furthest corner of the basket and had wrapped his knees in his arms, as if he could protect himself from the bullets that way. He was moaning, ‘Dear God, please save me. Save me.’

The German pilot had the balloon lined up in his sights now and was heading straight towards Aimee, half a kilometre away.