I came to Oxford in winter, when the colleges wore their stone like winter clothing — heavy, unglamorous, holding heat with the stubbornness of old money. My name is Julian Ashworth-Cross. I translate Portuguese poetry into English for a living, which means I spend my days negotiating between what words say and what they mean, which is to say, I make a professional habit of listening to things that refuse to be heard.

Margaux Duval-Lacombe was dead for eleven months when the parcel arrived. No return address. Just her handwriting on the front — the precise, slightly slanted script she'd used on every note she ever left me, from the first seminar on Donne at Trinity to the last text message she sent from a hotel room in Lisbon, three days before the accident.

Inside the parcel: a single dried root, wrapped in brown paper and twine.

Not medicinal. Not decorative. Something older, or something pretending to be older — a tangle of dark fibres, thin as hair and twice as persistent, curling into itself like a question mark that never found its answer. It was the colour of weak tea left too long in the cup, of autumn leaves on the Isis when the fog comes up fast enough to steal your bearings.

Beneath it, a folded sheet of paper with seven frequencies, each paired with a location. Forty-four point zero hertz, the gatepost. Three hundred and ninety-six point five, the stone bench. Five hundred and twenty-eight, the well. Four hundred and thirty-two, the old oak. Three hundred and forty-one point seven, the mirror pool. Two hundred and eighty-five, the garden wall. Five hundred and nineteen point three, the empty shed.

And a final line, written in a different hand — Margaux's lawyer's hand, or perhaps the courier's, or perhaps Margaux's own, written on a day she knew she would need a final instruction to travel without herself: Walk them. Not for me. For the root. It remembers what you've forgotten.

I don't know why I started at the gatepost. Maybe because the instructions were ordered, and ordering is what I do. I translate. I take something that exists in one frequency — one language, one emotional register, one skull — and I translate it into another without killing it. That's the promise, anyway. The reality is closer to smuggling.

The gatepost in question belonged to a house on Banbury Road that Margaux had owned for seven years and visited perhaps three times. She'd bought it as an investment, or so she said. I suspected she'd bought it as an insurance policy against her own disappearance — a place where something of hers could remain when she was gone, even if she couldn't.

The gatepost stood at the end of a gravel drive choked with dead ivy. I pressed my palm against its fluted surface — Cotswold stone, damp with November frost — and listened.

I'm not a particularly sensitive person. I don't hear frequencies. I don't feel auras. But at forty-four point zero hertz — exactly A above middle C, the note that tuning forks are cast in, the pitch that orchestras agree upon as a fiction worth believing — something shifted in the air like a fish turning in deep water.

I closed my eyes. And in the closing, I heard it: not a sound, but the memory of a sound. Margaux humming in the kitchen of her flat above the bookshop on St Clement's High Street. She was always humming. I'd never known what she was humming, but now, standing at the gatepost with the root burning a hole in my coat pocket, I recognised the frequency. It was exactly forty-four point zero. She'd been humming this house before she'd ever been inside it.