Hope pulls her green coat tighter around her shoulders. Today is the day.

The boat bumps over choppy waters, prow dipping and diving, to the island where time stands still. A living museum. Old houses and dirt tracks, no cars, no televisions, no signs of contemporary, hugger-mugger life.

The ferry slows and Hope’s heart speeds up. She hopes she has the courage to see this through. She is the only passenger. It’s cold and it will be dark soon. The captain pays her no attention. She imagines him waiting for his solitary passenger to return, coming onshore to look for her, then calling for help.

Hope walks onto the pier. She pauses, then turns to her right. Small steps, collar up against the wind. In her bag, a photograph of a woman called Hope with the best friends she can’t remember.

Now she can see the stone outline of the South Battery. She reads the date carved in the pale grey stone sign set into the red brick: 1812. Ten-foot high double doors, reinforced metal, are decorated with rows of round iron studs. Hope pushes, they open and she slips inside to the panelled hall. The dark musty smell of a building long abandoned rushes to meet her. Up the wooden stairs to the ballroom. Chandeliers, a bevelled dresser, arches of mirrors on each of the walls beside the marble fireplace. Hope shivers. She is in the right place. Imagining, suddenly, cinched waists and crinolines, fans and swirling, twirling satin and pearl as ladies spin, dance and float.

Hope puts her bag on the floor, crouches down and takes out what she needs. A bottle of wine and pills, a written apology to whoever finds her. She looks at the photograph of her friends one last time, willing it to come to life. To mean something. It doesn’t.

Then, she sees it, reflected in the flickering dusk light in the mirrors that clothe the ballroom. A sparrow, lying dead on its side on the parquet floor. Hope feels a stab of pity. Then, a prickling on the back of her neck. She’s certain there’s someone behind her. She spins round, but there’s nothing. Again, out of the corner of her eye, a movement. She turns back and sees, in the infinitessimal moment between one beat of her heart and the next, a reflection in the mirror.

Hope takes a step forward, lifts her hand and presses it against the glass. Recognising the silhouette. Her hair brushing her shoulders, like it used to, her favourite coat from MNG with the fake fur collar, the black Uggs. Herself, as she looked on the day of the accident. Her own eyes staring back at her. Hope jolts, steps back, mouth dry and heart racing.

Imagination, a flashback, she doesn’t understand. But she knows she is no longer alone. There are others in this abandoned ballroom with her, ghosts or figments of her imagination, she can’t tell, but they are there in the shifting of the air. Hope forces herself to look again, to look hard at herself. And, this time, she sees her reflection changing, growing stronger, her outline clearer now. That blue coat becoming green. She raises her hand to her head, her short brown hair, cropped for the surgeons. The pale scar above her right eye, like an exclamation mark.

Finally, she understands. Her old self – kept safe with her memories – is not dead, just buried deep. Hope looks at her two selves, merging and shifting into one, and now sees there are figures behind her. If she turns, they will vanish, but she recognises them. Remembers everything about them, her best friends since secondary school – every boyfriend crisis, exam catastrophe and career change. Hope touches her cheek and feels her skin is wet. Remembers. Of the four of them, she’s always the one to cry first. The girls are not there, of course they’re not, but she knows they’ll be waiting back in London.

At home. Hope doesn’t know why this strange, timeless place should have brought her face to face with herself – saved her from herself – only that it has. It will be tough but, with her friends beside her, she’ll be all right. She smiles at the Polaroid image and tears the letter in two. As she turns to walk away, Hope notices the sparrow, too, has gone. No more ghosts.

Citadel by Kate Mosse (£20, Orion Books) is out now

Illustrations: Daniela Jaglenka Terrazzini

Click here to read other Christmas stories written exclusively for Stylist

Governors Island by Kate Mosse