Frank plugged the system into the mains and began to explain how the test should work, the test that had so far failed each time. ‘You see, sir . . .’ he began.

‘For Christ’s sake man, just get on with it,’ Rowe snapped.

Sweat broke out on Frank’s brow and his hands trembled as he turned the system on. The line on the screen flickered into life. ‘Operate friendly craft signal,’ he said, flicking another switch. This was the moment when the line should start to show a deep double V that would be clearly visible on the screens installed into other Allied forces’ planes nearby.

After a few seconds the line quivered and took a sharp downward dive, and then another. The ‘friend or foe’ signal was clear for all to see. Frank’s mouth gaped open for several seconds before recomposing into a triumphant grin as the room erupted in spontaneous applause.

Dr Rowe was circling the room, shaking hands with everyone. ‘Good work, chaps. Soon be ready for testing in the field, then?’

After he’d gone, Frank took out a handkerchief and wiped his brow. ‘Bloody hell,’ he said. ‘That was a stroke of luck.’

‘Not luck, Frank,’ Vic said, his heart hammering in his chest. This was the moment of confrontation, and he had no idea how Frank would respond. He went to the cupboard, opening the door. ‘This is the old kit. The set on the table, the one that works, is ours, reconfigured and recalibrated by Scott and me to the mathematical model that you dismissed when we suggested it two weeks ago.’

He would remember for a very long time afterwards the expression of utter astonishment and shock on Frank’s face. The man began to bluster, but it was too late. Everyone ignored him, gathering around Vic as he unfolded several sheets of paper showing his calculations.

‘You’re an effing genius, Mac,’ one said.

Much later that evening, just as he was preparing for bed, there was a knock on Vic’s door. It was Frank.

‘I’ve come to thank you, Mac,’ he said. ‘For saving our bloody bacon. Can I buy you a drink?’

The gall of the man, trying to buy his favour with a drink. ‘It’s been a long day, so not for me, thank you.’

‘No hard feelings?’

This was the moment Vic had been waiting for – his opportunity to tame the snake forever.

‘Only on three conditions,’ he said, trying to keep the tremor from his voice. ‘Firstly, you have to listen to other people’s views as well as your own, in future.’

Frank ventured a conciliatory smile. ‘Point taken, old man.’

Vic pressed on. ‘Second. You never, ever dare to question my loyalty to this country.’

The smile disappeared.

‘And third, if I ever, ever hear you suggesting that I was anything to do with that leak . . .’

A long moment passed. Vic felt his fury rising.