The house on Walcot Street is clothed in darkness, its parlour curtains drawn tight against the light of the street lamps. A mere passer-by would think all of the inhabitants were long asleep.

Agnes raises her fist to knock on the door, but she cannot quite bring herself to let it fall.

What if she peers beyond the veil and sees a sight she is not able to bear? It is not too late to turn back. She really should. But there is a nightmarish inevitability to her actions. Somehow she knew she was going to come here, from the moment she first heard Mrs Boyle mention the White Sylph.

Releasing her breath, she finally knocks.

As before, Miss West steals noiselessly to answer the door. That is the one aspect familiar to their last meeting. Tonight the young woman is dressed from head to toe in jet, her flaxen hair extinguished by something like a widow’s cap. The only feature alive in her face are those simmering, witchy eyes. Their expression is far from friendly.

‘Miss Darken. Good evening. Do step inside.’

This is not the woman Agnes spoke to about the corpse. She is a polished version with better diction. Speechless, Agnes follows her into the house, which is even darker than on her previous visit. A powdery, sickly aroma overlays the rot she detected.

As she turns into the parlour, she sees bunches of open lilies glowing like pale, white hands by candlelight. Lilies and wax – that explains the cloying scent.

‘May I introduce the White Sylph?’ Miss West gestures to the far side of the circular table, near the drawn curtains.

For a split second, Agnes thinks she has already glimpsed a ghost.

The child sits behind a flickering barrier of black candles. She is an albino, entirely without pigment. A white gown bleeds seamlessly into the alabaster of her skin and ivory hair falls loose over her shoulders. Her lips and brows must be powdered, for Agnes cannot make them out. Even the girl’s eyes show clear as glass marbles.

‘Come. Be seated.’ Miss West has the air of a housekeeper revealing hidden rooms. She sweeps Agnes effortlessly towards a chair she does not want to take; there is no resisting her.

The White Sylph watches with uncanny serenity. She must be even younger than Cedric but there is an agelessness to her: it does not feel like sitting opposite a child.

Miss West takes the third chair, closing in the circle.

The Sylph reaches out and offers Agnes her bloodless palm. It is cold to the touch. By contrast, Miss West’s feels warm and dry.

There is no escape. Agnes is in their power now.

‘We’ll start with a hymn,’ says Miss West. She opens her mouth and sings.

Jesus, full of truth and love,

We thy kindest word obey;

Faithful let thy mercies prove;

Take our load of guilt away.