For me, one of the weirdest things about magic was the way some formae went out of fashion. And a good example of this is aer, which strictly speaking is Latinised Greek and is pronounced ‘air’ and means – well – air. Once you’ve mastered it, and that took me six weeks, it gives you ‘purchase’ on the air in front of your body. But since there’s no actual physical way of measuring the effect, and believe me I tried, your master has to be present to tell you when you’ve got it right. Once you’ve mastered it, you’ve got a forma that’s tricky to do and has, apparently, no effect. It’s not hard to see why it went out of fashion, especially since it was clear by the eighteenth century that it was based on a completely erroneous theory of matter. Nightingale took the trouble to teach me aer because, combined with the equally tricky and out-of-fashion congolare, it creates a shield in front of my body. Both formae were developed by the Great Man, Isaac Newton, himself and have the trademark fiddliness that has led to generations of students writing variations of WTF in the margins of their primers.

‘Isn’t a shield useful?’ I’d asked.

‘There’s a much more effective fourth-order spell that creates a shield. But you’re at least two years from learning that,’ said Nightingale. ‘I’m teaching you this against the chance that you may encounter the Faceless Man again. This should give you some protection from a fireball while you stage a tactical withdrawal.’

By which he meant run like fuck.

‘Will it stop a bullet?’ I had to ask.

Nightingale didn’t know the answer. So we bought an automatic paintball gun, attached it to a hopper feed and a compressor and mounted it on a tripod at the shooting end of the firing range. To start my training sessions I don my Met-Vest, my old school jockstrap and my standard issue riot helmet with face mask. Then I set the mechanical timer on the gun and walk up the range to stand at the target end. I always feel uncomfortable standing at the wrong end, which Nightingale said was just as it should be.

The timer was a relic of the fifties, a Bakelite mushroom with a dial like those on a safe except painted pink. It was old and flaky enough to add an exciting element of uncertainty to when it would ring. When it did, I cast the spell and the paintball gun would fire. Originally me and Nightingale had thought we’d have to jury-rig a mechanism to randomly vary the aim. But the gun jiggled so violently on its tripod that it produced a spread wide and random enough to satisfy the most exacting standards of the Imperial Marksmanship School.