‘Nah,’ he said. ‘All we know is they’re tight as ticks, which means for certain that whatever they’re doing over there is grade one top security.’

It niggled her, not knowing what was happening right on her doorstep. What exactly was so secret about it that they needed a guard on the gate and barbed wire all over the walls? And what on earth was that enormous mast?

Pa was sceptical when she asked if she could borrow his binoculars. ‘The marshes are good for migrating birds at this time of year,’ she said, repeating something she’d overheard in the cafe. He raised an eyebrow, but agreed to lend them and showed her how to focus each eyepiece. On her next day off, she packed them into a shoulder bag along with a bird book from the library.

On the ferry she chatted to Charlie Brinkley about birds. With his mind on the tide, he paid little attention, but at least he’d make a good alibi should anyone question her. On the Bawdsey side she followed the road around towards the marshes and then slipped off to the right, under cover of the area of scrappy woodland that bordered the Manor’s grounds.

Getting within sight of the buildings turned out to be more difficult than she’d expected. Brambles tore at her legs, branches whipped her face and fallen trees caused her to make several diversions, but she pushed on until she encountered a chain-link fence a full six feet high topped with evil-looking coils of barbed wire. Walking along the perimeter, she eventually discovered a point at which she could see through the undergrowth the back of what looked like a stable block, and beyond that, the base of the tall metal mast.

She focused the binoculars as Pa had shown her. At first, the place looked deserted. The mast itself appeared much taller and wider at its base than she had imagined. At the top was a platform, and halfway up – hold on a sec – a tiny speck was moving. She focused again and saw that the speck was a man, climbing down a flimsy-looking ladder.

A heavy hand on her shoulder made her yelp with fright, nearly dropping the binoculars.

‘Excuse me, missy. I’m afraid you will have to come with me.’ It was a tall, burly man in uniform with a gun holster slung beneath his arm.

‘I was looking for birds,’ she stuttered.

‘And just what kind of birds can you see over there?’

‘Ermm, blackbirds, and robins, and . . .’ Her mind went blank.

‘I’m afraid you’re not exactly convincing me, miss. This is a top secret facility, and we take any breaches of security very seriously. Very seriously indeed. Now hand over those binoculars. You’re coming with me.’

When she hesitated, he grabbed them from her.

‘Now, do as I say or I’ll have to handcuff you.’

His hand was at the small of her back, propelling her forward.

‘Am I being arrested for birdwatching?’