And it was at this point that I noticed something peculiar about the letter, one more of its strange and, for the moment, inexplicable traits. As I held the paper to the light I realised that the author had folded the paper twice and sealed it not with wax but a rust-coloured shellac. This was not unusual in itself, of course: most people, myself included, sealed their letters by melting a stick of shellac. But as I gathered the flakes and tried to reconstruct the image impressed by the matrix I noticed how the shellac was mingled with a substance of a slightly different colour and composition: something darker and less adherent.

I moved the letter into the beam of light falling across my counter. Monk's broom rasped slowly across the floorboards, and I became aware of his curious gaze. I prised at the seal with the blade of my penknife as gently as an apothecary slicing the seed pod of a rare plant. The compound crumbled and then sprinkled over the counter. A beeswax was clearly distinguishable from the shellac into which, for whatever reason, it was mingled. I carefully separated a few of the grains, puzzled that my hand seemed to be trembling.

'Is there something wrong, Mr. Inchbold?'

'No, Monk. Nothing at all. Back to work with you now.'

I straightened and gazed over his head, out of the window. The narrow street was busy with its morning commerce of bobbing heads and revolving wheels. Dust was raised from the carriageway and, caught in the slats of morning sunlight, turned to gold. I lowered my eyes to the flakes on the counter. What, if anything, might the mixture mean? That Lady Marchamont's matrix bore a residue of wax? That she had closed another letter with a beeswax only moments before sealing mine with shellac? It hardly made sense. But then neither did the alternative: that someone had moulded her original wax seal, broken it, then closed it with shellac impressed by a counterfeit seal.