He’d steeled himself for visiting the receiving room, dreading flashbacks to that overheated wooden shed with its new paint fumes on the terrible day when Johnnie died. But this enormous bunker, with its mingled smells of fresh concrete and cigarette smoke and the array of new pieces of kit that he’d helped to design, was astonishing – almost overwhelming.

To his relief, all the faces were strangers. ‘We’ve come to look at the IFF system,’ he said. ‘How’s it doing?’

‘Bloody hopeless,’ one of the girls replied. ‘Hasn’t been working for twenty-four hours now. Hope you’re going to fix it?’ It was a posh voice, confident and imperious, the sort he remembered from the older boys at boarding school. Her face registered a flash of recognition. ‘Hold on a tick. Do I know you?’

‘Vikram Mackensie,’ he said. ‘How do you do?’

Her eyes twinkled with an expression he could not quite discern. ‘Marcia Bonham. I am most pleased to meet you.’

They quickly discovered that the problem lay not with the kit in the bunker but in the calibration of the receivers, although why on earth the RAF engineers on site could not have worked this out they didn’t ask. At the workshop they found two engineers huddled over a blazing pot-bellied stove in a fug of cigarette smoke. Vic tried to explain the problem.

‘You’ll need to go up the mast to fix it,’ he said.

The pair looked blank. Vic knew they would be reluctant to take orders from civilians – indeed, they had the right to refuse – but it was worth trying. ‘The commander says it’s vital, lads. It must be fixed tonight.’

‘It can’t wait till morning,’ Monty added.

‘We’re not qualified,’ one said, clasping his mug. ‘Need to ask the boss.’

‘Then where is he?’ Vic snapped. ‘Go and find him at once.’

The man shrugged and hauled himself up from the stool. ‘On leave. Sir. Back tomorrow. Sir.’ He gave an insolent half-salute.

Vic and Monty exchanged glances. They had two alternatives: disturb the commander and ask him to order the engineers up the mast – and even then, have to trust that they wouldn’t make the problem worse – or . . .

‘It’ll have to be us, then,’ Monty said.

‘Ever done this before?’ Monty asked, peering up into the blackness from the base of the mast. The moon was half full and still visible, but a cloud bank was fast approaching from the east. They’d borrowed overalls, torches and a small bag of tools, now slung from his waist.

‘Just the once,’ Vic said, starting to climb the ladder, its rungs slick with damp. Go for it, old man, Johnnie whispered in his ear. One step at a time. No problem. He shouted encouragement to Monty, following close behind: ‘Nearly there, mate. Just a couple of dozen more steps.’

Just as they arrived at the top, the moon disappeared and Vic’s torch died. He cursed, giving it several whacks on his palm, but it made no difference. Monty’s was also fading fast.