‘Of course, everyone does.’

Watson-Watt stopped and turned to face him. ‘The thing is that it’s not just icebergs or shipping we’ll need to detect, it’s aeroplanes. Of course there will be tanks and artillery on the ground, but any future war will be won or lost in the air. There are already reports of Mr Hitler amassing hundreds of them, and that can only mean one thing: he’s planning to drop all kinds of hell – high explosive, incendiaries, poison gas – onto our cities and factories. And our people. It will be an altogether different kind of warfare, more terrifying and just as deadly. We have to find a way to stop them.’

He took his seat again, leaning forward with his legs crossed beneath him like a coiled spring, and lowered his voice confidentially. ‘What we’re doing here has never been done before anywhere in the world, Mackensie. Imagine a vast spider’s web suspended in the sky between us and Europe.’ He drew a wide circle with his arms. ‘Now, think of that web as being made of pulsating radio waves. It’ll be completely invisible, and undetectable – but as soon as anything tries to penetrate it, we will know, in time to send up our own fighters to shoot them down.’

Vic found that he’d been holding his breath. He could see it all too clearly. Over the past few weeks he’d tried again and again to speculate what it was he’d been recruited for, and although he’d assumed it would be something to do with defence, he’d never for a moment imagined it might be anything as astonishing and ambitious as this. And he was going to be part of the team developing it.

‘It sounds bloody brilliant, sir,’ he breathed. ‘’Scuse my French.’

‘But does it work, you’re going to ask?’

Vic nodded.

‘The answer is yes, and no. Our first experiment was a near disaster, but we did actually manage to track a plane at around eight miles, which was enough for them to stump up some funding. We started in Orford, which is a desolate strip of sand just north of here; then, thank goodness, this place came up. Here we are, in paradise, I think you’ll agree.’

‘It certainly is the most beautiful place, s . . . Mr . . .’

‘Robert. But there are many problems, and that’s where you come in.’

For the next hour they exchanged ideas about how to solve the innumerable difficulties in developing such a system. Apart from the practical matters of finding the right places to set up transmitter masts and receiving stations and training staff to use the screens and interpret the blurry blips and squeaks they emitted, there were many knotty scientific problems: how to compress transmitters currently weighing several tons so they could fit inside a plane, how to make the equipment mobile, how to improve low-level coverage, avoiding confusion with church towers and the like – and, perhaps most importantly of all, how to identify aircraft as ‘friend or foe’.