The dull steel is freezing to the touch as I lift it from its bed of rags on the floor. To the casual observer, it looks no more menacing than an offcut of scaffold tubing, which is exactly what it is. A little bigger than a beer can, the tube is capped at both ends, and there’s a little hole that I’ve drilled in the wall of the cylinder – the detonation hole. Anyone expecting a black bowling ball with a sparking fuse poking out of the top would be very disappointed. Make no mistake – this is what a bomb looks like.

There’s this little book that lives on the top shelf in the spare bedroom. Issued to Gramps’s uncle, it has an olive-green hard cover and nicotine-yellow pages. It smells of history. In an unassuming typeface no bigger than all the text that follows, it is titled, The Home Guard Guide 1940. Among the tutorials on digging trenches in a hurry and sabotaging enemy communications, it’s full of advice on improvising explosive devices. I’ve browsed through it a few times over the years, idly imagining that it might be fun to build something from its instructions, but in recent weeks it’s become my bible. People understood back then. While men of fighting age were sent to the front, those too young still had a duty. It’s no good blindly going about your business when the enemy is among you – you have to fight.

I rest the thing on the workbench – pipe bomb number four.

My first attempt was a dud; I spent half an hour watching it do nothing at all from fifty metres away. Number two fired, but just shot a sheet of angry flame out of the detonation hole. The pair of them share a shallow grave in Perrett Woods. Number three is responsible for a crater a metre and a half wide, and a series of posts on Facebook asking if anyone else heard that noise. I still have the remains of it: a blackened and jagged sheet of steel that was once a sealed cylinder, smelling like rotten eggs, looking like a torn tatter of the thinnest fabric.

Standing on the edge of that blast hole, under cover of darkness and a wood in fresh bloom, I came face to face with the destructive intent of what I’d been building. My delight at a successful firing ebbed as the minutes passed, replaced by a swelling panic. I’m certain I would have just levelled the ground and left the project behind right then, filed in my mind as an idea too bold for my weak self, had it not been for Sophia. Her wild-eyed smile never abated the whole time we stood there. She squeezed my hand in hers, small and soft. ‘You’re so brilliant,’ she said.

My current version shares the blueprint, only it’s bigger.