There, less than a metre below, a young man was staring up at me. He was hanging from a ladder that led down into the darkness of the shaft. He must have been frozen there hoping we wouldn’t look down. I didn’t get more than a glimpse in my helmet light, of a pale face with big eyes framed by a black hoodie, before he let go of the ladder and fell.

No, not fell. Slid down the shaft, hands and feet jammed against either side to slow his descent. As he went, I heard a noise like a room full of whispered conversations and felt a burst of imaginary heat as if I’d stepped out into hot sun.

‘Oi,’ I yelled and went down the ladder. I had to. What I’d felt had been vestigia and what the guy had done, slowing himself down without friction burning his hands off, had been magic.

I heard Kumar call my name.

‘He’s down here,’ I shouted, trying to skip rungs and then jumping the last metre. The impact of my landing drove the accumulated water in my wellies up into my groin – fortunately it was warm.

Another short narrow corridor. I saw movement at the far end and followed. The air was full of the sound of rushing water. Common sense made me skid to a halt at the end, just in case the guy was waiting around the corner with an offensive weapon. The corridor opened into a barrel-vaulted tunnel. To the right, water cascaded down a weir and to the left I saw my guy, bent under the low ceiling, water up to his hips – wading away as fast as he could.

I jumped into the water behind him and the current swept my legs out from under me and landed me on my back. What can only be described as highly diluted poo washed over my face and I shoved myself back up fast enough to crack my head on the ceiling. If I hadn’t been wearing a helmet I probably would have killed myself.

I staggered forward, vaguely aware of splashing behind me which I hoped was Kumar or Reynolds. Ahead, the man in the black hoodie was making for what looked like another intersection. He glanced back, caught sight of me, and suddenly turned, raising his right hand. There was a flash, a painfully sharp retort and something zipped past my ear.

The big difference between green and experienced soldiers is that until you’ve actually been shot at once or twice, your brain has trouble working out what’s going on. You hesitate, often for only a moment, but it’s the moment that counts. I was green as snot but fortunately Special Agent Reynolds was not.