‘But you’re not,’ he said.

‘No, but Maman has an idea about that. She’ll explain when she’s made us some dinner. Are you strong enough to walk over to the farmhouse?’

‘For your mother’s mutton stew I’d run there,’ Marius laughed.

25 August 1918: The school, Bray

General Bruce closed the door after checking there was no one close enough to listen. The school roof had been damaged when the Canadians took the town and the ceilings had cracked and plaster dusted the floors. Still the army had moved back in.

‘So, Captain Ellis, the German boy is safe?’

‘He is, sir. He’s been very useful. He was pretty sick when Sergeant Grimm called that Benedict but he heard enough to be able to give us priceless secrets.’

‘Such as?’

‘The main thing this Benedict said is that the Germans are calling our 8th August attacks their Black Day. And they are blaming it on our tanks. They are losing heart for the fight.’

General Bruce gave a tight smile. ‘Yes, I watched the tanks in action at Amiens. They just rolled towards the German machine guns and ploughed through them. Wonderful to see. Lots of enemy soldiers just throw away their guns and give up as soon as they see one of our tanks coming.’

‘The Germans would give anything to know how to stop our tanks next time. Anything. If Sergeant Grimm can pass on plans of the Mark Five tanks or the Whippet tanks – and show the weak spots – then they will pay Silver Hand and Benedict ten thousand marks each,’ Captain Ellis said quietly.

General Bruce nodded. ‘Do we have any plans?’

‘Yes, they’re in the safe.’

‘And any notes about weak spots?’

Captain Ellis was almost whispering. ‘Yes, we have those too. The men are saying it gets very hot inside the tank. They have to leave hatches open to get enough air. If the Germans use gas shells on the tank drivers the gas will get in and the crew will choke.’

The general shrugged. ‘They can put on their gas masks can’t they?’

‘A tank crew work as a team – they need to work together with the commander to decide which direction to go, the driver to change the speeds, the gearbox men to turn left or right, the gunners to take aim and fire. They are stuck inside a metal box alongside a roaring engine. They have to shout to work together. If they put on gas masks they can’t talk. Gas shells will make them almost useless as fighting machines.’

General Bruce nodded. ‘I see. The Germans mustn’t find that out. Maybe it’s time to arrest Sergeant Grimm.’

‘We still don’t have any proof he’s a traitor. And remember he’s a bit of a war hero with that silver hand of his.’