The wall around the perimeter was child’s play. Six foot, but no spikes or barbed wire on the top. Barbed wire is my nemesis.

There’s a reason they use it in war zones.

At five foot two, I couldn’t quite reach to pull myself up, so I scaled a nearby tree with a sturdy branch overhanging the car park, lowered myself until my feet made contact with the top of the wall, and then ran softly along it to a place where I could drop down out of sight of the CCTV cameras that circled the building at intervals.

On the other side of the car park was the fire door Gabe had described, and it looked promising. A standard half-glazed door with a horizontal release bar on the inside. I saw with satisfaction that it was poorly fitted, with a gap at the bottom that you could practically get your hand through. It was the work of about thirty seconds to slip my long metal slider underneath, swing it up so the hook caught on the bar, and pull firmly down. The door opened, and I held my breath waiting for the alarm – fire doors are always risky like that – but none came.

Inside, the lights flicked on automatically – big fluorescent squares in a tiled ceiling that stretched away into the darkness like a chess- board.

The far end of the corridor was still pitch black, the sensors there not yet picking up my movement, but the section I was in was bright as day, and I stood letting my eyes adjust to the glare.

Lights are a bit of a double-edged sword. On the one hand, they’re a huge red flag to anyone monitoring the security cameras. There’s nothing like a screen lighting up like Christmas to catch a security guard’s eye and make them glance up from their phone. But you can sometimes style it out if you’re caught walking confidently around a building at night when the lights are on. It’s much harder to explain your presence if you’re creeping along an unlit corridor with a torch.

You might as well be wearing a striped T-shirt and carrying a bag marked LOOT.

Right now it was 10.20 p.m. and I was wearing my ‘office’ clothes – black trousers that looked like they could be the bottom half of a suit but were actually stretchier and more breathable than any regular office wear, a dark blue blouse, and a black blazer that was standard off-the-peg from Gap. On my feet were black Converse, and I had a grey Fjällräven backpack slung over my shoulder…

Continue reading the extract here…

Buy a copy of Zero Days here.