And what do Nightingale and I have to measure vestigia with? Sod all, and it’s not even as if we know what we’re trying to measure in the first place. No wonder the heirs of Isaac Newton kept magic safely under their periwigs. I had jokingly developed my own scale for vestigia based on the amount of noise Toby made when he interacted with any residual magic. I called it a yap, one yap being enough vestigia to be apparent even when I wasn’t looking for it.

The yap would be an SI unit, of course, and thus the standard background ambience of a Central London pub was 0.2 of a yap (0.2Y) or 200 milliyaps (200mY). Having established that to my satisfaction I finished the half-pint and headed downstairs to the basement, where they kept the jazz.

A set of creaky stairs led down to the Backstage Bar, a roughly octagonal room, low-ceilinged and punctuated with stout cream-colored columns that had to be load bearing because they certainly didn’t add to the sight lines. As I stood in the doorway and tried to get a feel for any magical ambience, I realized that my own childhood was about to interfere with my investigation.

In 1986 Courtney Pine released Journey to the Urge Within and suddenly jazz was back in fashion and with it came my dad’s third and last brush with fame and fortune. I never went to gigs, but during the school holidays he used to take me with him on visits to clubs and recording studios. Some things linger even from before conscious memory—old beer, tobacco smoke, the sound a trumpet makes when its player is just getting it warmed up. You could have two hundred kiloyaps of vestigia in that basement and I wouldn’t have been able to separate them from my own memories.

I should have brought Toby. He would have been more use. I stepped over to the stage in the hope that proximity might help.

My dad always said that a trumpet player likes to aim his weapon at the audience, but a sax man likes to cut a good profile and that he always has a favorite side. It being an article of faith with my dad that you don’t even pick up a reed instrument unless you’re vain about the shape your face makes when you’re blowing down it. I stood on the stage and adopted some classic sax-player stances, and as I did I began to feel something, stage front and right, a little tingle and the melody line of “Body and Soul” played far away, piercing and bittersweet.

“Got you,” I said.