‘They’ll hang you for this, you mad bastard,’ yells Kincaid in his ear. ‘He’ll say you made him do it. Made him ferry you out here. And if it comes to it, I’ll say the same. You had me at gunpoint. Made me come, when I was all for calling in back-up and telling the bosses …’

McAvoy turns away from him. Fixes his eyes on the little black square on the horizon. It’s been getting steadily bigger. He swivels back to look at the distant shoreline. It’s just a smudge now: a line of lights, like the last embers in a dying hearth.

‘McAvoy,’ shouts Kincaid, again. ‘I said, they’ll hang you …’

‘I heard you,’ he growls, his voice snatched away on the wind. The boat lurches as a hard wind hits them side-on. Overhead, gulls whirl against the ugly, badly Artexed skies. The clouds are great cakes of sun-bleached cowshit: all whorls and vortexes.

Stay, Fin. I’m coming. Whatever it takes, you fight. You fight to live, and I swear, I’ll get to you …

A burst of static, sizzling like hot oil.

‘RNLI station at Cleethorpes,’ shouts Barrington, behind them. ‘On the radio. Reports of a small craft near the base of the fort. They know about our break-in and wanted to check the description. What do I say?’

McAvoy wipes the salt water from his face. Turns his back on the rain and gives Barrington his attention. ‘You say thanks and you tell them you’re on a training exercise. You’ll redirect towards the fort. If they offer to lend back-up, you politely decline.’

Barrington licks his lips. Nods. Lifts the receiver and does as instructed. McAvoy turns to the horizon. The fort emerges from the grey. He narrows his eyes. Makes out the shape of a building he has seen so many times from the shore.

‘Like something from a film!’ shouts Kincaid, nervousness in his voice. ‘Christ, how did they build it? What’s it even for?’

McAvoy ignores him. He can’t seem to find the right words. He knows all about the forts. They were built a century earlier: great, forbidding armour-plated castles constructed to defend the Humber from German U-boats. They’ve stood empty for decades, their steel skins turning to rust, their concrete struts barnacled and slimed by the waters that lap at its great grey belly.

‘You still think you can get through all this without anybody you care about doing time? You’re a fantasist, mate. I’m on your side, but there should be a whole tactical team with us! He’s insane, McAvoy. Insane and very good at killing people. What have you got? You’re not even armed!’

McAvoy doesn’t respond. Hears a clatter from behind him and spins around to see Barrington holding out a hard plastic toolbox, the lid flipped open. ‘Take your pick,’ he yells, as the wind screams around them.

‘Are you people fucking mental?’ yells Kincaid, despairingly. The boat slaps down again, and he lurches right, retching and heaving over the side.