Katherine fiddles the horsehair over the brass screw on the tendiculum and attaches it to the other end. Then she winds it tight over its polished rosewood point. The hair bites into the inflamed and crusted flesh around the puckered mouth of the fistula.

She asks Geoffrey to come around and hold it still while she finds the snouted needle, about a foot long, with a groove running its length. She slips this into the hole, following the line of the horsehair. Blood and something else leak out and run on to her shoes.

‘Right,’ she says. ‘This is it. Thomas, be ready. Richard, can you bring that sponge? And Geoffrey, hold the candle steady.’

All three nod, Richard clutching a sponge stained red with wine, thickened by rose oil and egg albumen.

‘When I have made the cut,’ she says, ‘we must first mop the blood. We need to clean the channel as far as is possible. Then we must sit him up so that he presses down on the wound and we must wake him and feed him meat and wine.’

Sir John is still snoring. Drool stains the sheet under his mouth.

She feels in the dish of wine for the scalpel. It is bone handled, beautifully made, the sharpest thing she has ever seen. She touches it to the needle and then slides its blunt edge into the groove.

She gives Thomas a nod and then begins.

Thomas reminds her to insert the cochlea.

She stops.

The cochlea. Of course. She finds the little ivory spoon in the wine, and inserts it carefully into Sir John’s anus. She turns it and then takes the snouted needle and taps it against what she hopes is the cup of the spoon. This will stop her cutting too far, cutting into the rectum.

She returns to the scalpel and nudges it towards the flesh. After a moment’s hesitation, the skin splits. Blood wells into the cut. She slides the scalpel down, parting the skin and the layer of pale waxy fat below. Blood fills the cup of her hand. She can see no detail of what she is cutting.

‘The sponge! Clean the blood away.’

Richard wipes it away and the wound is clear for a moment. She finishes the cut. Feels the tap of the scalpel against the cochlea. The tendiculum comes free in her hand.

‘The sponge.’

Richard applies the sponge, smearing the blood. Katherine drops the needle and the scalpel back in the wine.

‘Give me that,’ she says and takes the sponge. She holds it against the wound, wiping away shreds of black corrupted flesh, cleaning the scar of the fistula.

She discards the old sponge and finds a fresh one to press against him.

Sir John is twisting on the bed.

‘Quick,’ she says. ‘Sit him up.’