Rep is a legend, the Macavity of the City. He has a mystical understanding of the London market. If you’re the finance director of almost any big British company looking to buy up a slice of a rival, you will tap him up for advice. He’ll know where to find the stock, what price to pay, and how to execute the deal before anyone notices.

‘Forgive the eccentricity of this meeting,’ he says, in clipped vowels, ‘all this cloak and dagger stuff. We’re going to walk for about ten minutes and we can talk when we reach our destination. If you could stay a few yards behind me, just so that it’s not too obvious we’re together?’

This is even odder than I expected. Are these precautions because of what happened to Clare? Is he in some way the cause of what happened to her? I’m on hyper alert, repeatedly checking over my shoulder and glancing in every shadowy doorway as I follow Rep east through Liverpool Street station. He goes at a brisk clip, taking the stairs two at a time. I almost break into a jog to keep up.

He crosses the vast cavern of the station and bounces up the stairs to Bishopsgate. Even at this time of night, we have to dodge cars and vans to cross, walking a diagonal to veer north. We pass the new pseudo-Palladian buildings that have been erected as a classical veneer for the Wall Street barbarians who’ve taken up residence. Then we speed-walk around the rundown perimeter of Spitalfields market till the white spire of Hawksmoor’s magnificent Christ Church looms. We are now on Fournier Street as we enter seventeenth century Huguenot London. I can smell the faintest aroma of Bangladeshi curry drifting down from the cafés of Brick Lane.

Rep stops outside number thirty-three, a flat-fronted, red-brick Georgian terrace, with stucco pilasters framing the door. He unlocks it and goes inside, leaving the door open. Feeling more than ever as if I’ve walked into a John Buchan novel, I check left and right to be sure I haven’t been followed, then enter.

It’s dark and freezing. I can hear movement on the floor upstairs, which I assume is Rep, though just at this moment anything seems possible. My heart beats faster as I climb the bare wooden stairs. From what I can see, the house is derelict. There appears to be no electricity and the panelled walls are patchy and peeling.

‘Wait there,’ Rep says, as I reach the landing. He’s in a sparsely-furnished sitting room, lighting candles in dull brass sconces attached to the walls. They cast a flickering, yellowish glow over the room. We’ve stepped back two or three centuries.