We are spellbound.

There is no other way to describe it. Yes, we have all the magic we could ever wish for at out fingertips. We could do anything, anything with this, and yet the exquisiteness of this creature is enough to make Ann stop whining, Felicity stop freezing. She stops me thinking. Pure thoughts.

"Gemma. Ann. Felicity." The last name is said with extra force, somehow, although the voice is just as light and flowing as before. She cocks her curious head and surveys us out of those extraordinary eyes.

I never thought the words would pass my lips, but here they are: Pippa's beauty was coarse. Obviously, she is still far more beautiful than we could ever be, but as we now gaze at the entity in front of us, we are secretly, each one of us, comparing them in our minds. Pippa's nose could sometimes wrinkle in disgust, and it made her look ... less lovely. Her eyes were sometimes coated in malice and vanity that made her look very cruel. I would rather appear as I am, abundant in imperfections, than have the beauty of Pippa, in front of this creature. It would humiliate me.

"What ... who are you?" Felicity's voice is a whisper, a scurry of wind across dry leaves. The creature smiles – oh, that beautiful smile! – and reaches out, plays with a strand of Felicity's silver-gold hair. It terrifies me.

The creature is not human, and yet has human form. Her skin is smooth, fresh and perfect, pistachio green in colour. Her hair falls around her naked torso like seaweed, slippery and somehow iridescent. Eyes of dewy gold, flecked with green, the colour of fresh autumn. Lips, curving around creamy teeth, also shimmering with that half-oily slick that coats her. Green. She is green.

She smiles, once more, and looks at me. It is like staring into the river itself. I find myself drawing closer, and she leans forward and strokes the round of my face, plays with a tendril of loose hair. She twists it around her finger, and it looks like she has been cut, so vivid in the shade against her soft skin. Gaze down into the water that surrounds her. She is naked, completely so. Beautifully so. The curve of her waist, the gently undulation of her hips. The way her feet – and so curious they are – gently flow, slip past one another as she ... swims? Floats? What is it she is actually doing? Her fingers pass swiftly over my lips, and I taste them as the cool of her palm gently strays to my neck. They are rich, mossy, deep and delicious. Her eyes flicker languidly to Ann. Beckon her forward and make her fall in love with you, because you can. You so easily can.

The air smells light and thin as I step back. Felicity is scanning the river, a wild, hopeful smile on her lips. I hate to see her so very captivated. It is vulnerable. Weak.

"Gemma, who is she? What is she? Is she a mermaid? Don't you think it's odd that after all the time we've been here, we've never seen another living being? Do you think it's possible that Pippa sent her? Pippa sent her to look after us? Do you think it could be Pippa reincarnated?"

No. Pippa could never be this beautiful, however hard she tried. No. Pippa is gone, dead and living at the same time. Pippa will not come near us again, and we will not go near her. Yes, sometimes it feels as through the fabric between this world and the next is wearing thin, and sometimes I can hear her sweet young laughter, feel the shift of air as she dances close to me, catches my hand and whispers in my ear of her one true love. No. Pippa is dead and buried. This is not Pippa, nor has she been sent by our friend. Nor is she a mermaid, I am sure of it, because mermaids are ...well, half fish. Are they not?

"Are there others, Felicity?" My voice is raw and jagged. It scares me.

"Not that I can see ... I wonder what she meant when she said she'd been waiting." Felicity's eyes focus on me for the first time, and they seem wanting and scared. Hopeful.

"Felicity, I think we should ... should ... leave, Felicity." The magic of her gaze is wearing thin, and I can see through the veil now, she the way in which she is smiling and laughing with Ann. It's friendly. Sinister.

"You must be joking, Gemma. I'm never leaving. She's just so ... so..."

"Yes, she's beautiful. Yes, we can talk to her, but we have to leave at some point."

"Of course." She is not listening, glancing along and across the river, searching for more slick seaweed heads, petal –soft smiles and shining eyes.

"What is your name?" Ann whispers, and we are all listening.

"What is your name?" She replies, in a singsong voice. She laughs, and we look at each other. Unsure. Scared? Unsure.

"A...Ann. And this is Gemma, and Felicity."

"Ann. Gemma. Felicity. Pippa?"

Felicity swallows, looks at the ground. "Pippa is dead."

"Yes. I know. But do you?"

The question makes no sense to either Felicity or Ann, but I understand it. Pippa is gone. She is dead. Her corpse is slowing rotting to earth in a polished wooden box in unforgiving soil. No. It is not a pretty picture. But it not a picture either. It simply is. Pippa is not coming back. We will not see her again, and that is how it is meant to be. The dead move on, make choices. Ann knows. She knows better than anyone. Yet she doesn't see it. Neither does Felicity. Pippa. Is. Gone.

We say nothing. The silence stings like lemon juice. Her eyes find mine, and she bites her bottom lip. Her teeth flash.

"Gemma. Come and sit with me. Swim with me."

"No, thank you."

"Don't be rude, Gemma." I understand. It was not a question, a suggestion. It was an order.

"No."

"Gemma. Gemma. I understand, better than anyone. I understand, Gemma Doyle. Mary Dowd. Persephone."

These are not my names. I do not know them, and they are not my names.

"You look so much like Mary, dear Gemma. Not so much like Persephone, but then again, those Greeks were only guessing, weren't they?" she laughs, looks to me with a smile on that green face and the tinkle of merriment still hanging in the air.

"Persephone. Mistress of the underworld." Felicity looks towards me, accusingly. As though I gave the name to myself. As though I thought of the meaning, of the goddess behind the name, and decided it would make me powerful.

"Who's Mary?" I ask, ignoring the fiery holes that Felicity is boring into the back of my head.

"A girl you never knew. Worry not, my dear lady."

She is toying with us, all of us. Confusing us. At first, I thought she was seducing Felicity, touching her first, speaking her name with weight, with depth, that did not extend to Ann and I. But then ... they way she stroked my face, touched my skin, dragged those spindly fingers across my blushing lips. And then Ann. And now me, whispering silky words into my ears that I do not understand, but am desperate to fall in love with.

She stops smiling. A cloudy tear rolls down her cheek. It is murky and deep. River water. She is water. She is river.

"I am here to talk to you. All of you. About something very special. I am not meant to warn you, to approach. But I could not help myself. I have been exiled from my home, my tribe. My place in this world for hundreds of years."

"How old are you?" Felicity cannot help herself. Indeed, the girl looks no older than us, taut skin and supple bones.

"Older than you, certainly. Hundreds of years older than you. I have been here so long the river knows my voice. The water that is flowing over me has flowed over me before. Every little particle. Does that not terrify you?"

Yes. It does and it doesn't, at the same time. Ann hangs back, wary at the ambiguity. She is so very wary. Felicity is smiling that ripe smile, but I am sure I can see through it to the other side where question race like killers through the back streets of London. She is struggling. She is trying hard to piece together a question, something witty and certain, something prying. She is trying so very hard. I want to kiss her.

"You asked my name. Ann, yes? You asked my name?" She looks towards the trembling girl, who nods. Does not speak. I see the slight tremor escape her body. It rolls towards me in waves. Do not let it drown you.

"Yes, I can see why you would want to know. After all, I knew your names. I knew all about Pippa. Mary. Evelyn?" She looks to me and smiles, innocent. So far from innocent, and yet I cannot hate her. "Yes, Evelyn, wasn't it? Your sister. Oh, I watched her for so very long. I loved her as one can only love a child. I thought often of speaking to her, with her, but I never did. I don't quite know why." She is pondering, pensive, suddenly a thousand miles and sixteen years away from us. The gulf is black, and it is bleak. It speaks of ignorance and India.

"Yes. I never spoke to her. Well, she never strayed that close to the river. Not after the first time." That tinkling laugh again. It mocks us, and our grief. "Not after the first time, no. But when she was expelled from that water, she never wanted anything to do with it again. Not surprising, really. Not when you think about it."

This creature lived so close to my sister, for all those years. So close, and she thought she was alone. So close. Too close.

"I often thought about leaving the river and going to sit with her. I never did. I did not know what I could offer her, really. What can I do? I cannot dry her tears, look at me! I'm a river, aren't I? Made of water. Water, and dust, and smooth round pebbles. And occasionally little schools of fish. That's all. And I cannot sing, cannot dance, have no musical instrument. I did not think my stories would be of any help. Not to her. Not when she was so very lost already." She gazes round at us, impassively. I do not know why she is telling me this, but I am mesmerised. "I was beginning to wonder whether you'd ever come. Like she said you would. But then you did! And she was so very happy, and I was so very happy for her. But then you were clumsy." She looks me directly in the eye, and I want to look away but don't. "You were clumsy and unforgivable. She had been waiting for sixteen years, and you greet her with the news of her darling mother's death? Tut tut, Gemma. I expected better. The way she whispered about you, I expected a ... a magician. A sorceress. Not a ... what was that phrase he used?" she smiles at me, those milky teeth perfectly spaced and slightly pointed, "Not a 'silly little schoolgirl'."

I will not lie. It was not a dagger through my heart. Not a spear of ice. Not a deep dark cold. Just an electric heat that pulsated through me once, maybe twice, and then died down into something that spat and boiled occasionally.

"How do you know that? How can you say that?"

"Don't think I haven't been listening, Gemma. After all, I can cross the veil between life and death – just watch," and before we could stop her, still her or slap her, she was gone, undulating wildly through the rocky boulders and icy rivulets towards the waterfall. I did not call out "Stop!" I did not want her to. She was listening, all those nights ago, listening as he kissed me and touched me and made me moan. But which night was it? He said the words so very many times.

She slips under the waterfall like parchment under a door. And then there is that high, quivering moment, when you wonder whether any parchment will reappear, whether you will have contact with Beyond The Door that night. Whether your notes of loneliness will be answered, or whether they will lie on the cold dark floorboards all night, a new kind of solitude.

She comes back. Of course she does. Because whatever she is, she cannot die, can double back and live for hundreds of years. She's green, for Christ's sake! The woman is green.

"See? I told you so. If I can cross between life and death as easily as you can choose between – what was it?" she glances towards Ann, who falls back, mouth slack, "-jam and marmalade, well, then, it stands to reason that I can cross between this world and the next. Does it not?" she gazes round at us, her dewy eyes wide. They are watery, but not in the same way that Ann's are. Yes, water runs down her face constantly, out of those beautiful eyes and into the slippery folds of her hair, but she is not crying. She simply is made of the stuff, it seems. She cannot be crying.

"Does it not?" Oh. She is wanting an answer.

"Yes, of course." Felicity is there, determined to understand, determined to be the one to coax real words, real things, out of the creatures mouth.

"Felicity. You are wrong. I cannot cross between this world and the next. Yours. I cannot do that. But I can listen." She darts towards me, whispering on the gentlest breeze there is. The words reach me, and make sense. "I can listen, with my ear to the riverbed, and I can hear everything. Everything. I have heard what he does to you. What she-" she flicks her head towards Felicity, "-does to you. I can hear everything, but see nothing. Oh, but it does not matter, because I first saw you all ... so long ago, it seems like, now, but it cannot be as long as I imagine. Strange, how time plays tricks on you. Especially when you have so much of it." Laugh. Pause. Continue. "I put faces to the words and imagined it all. All apart from him. I had not seen him when he first became a regular occurrence. Had I? You hadn't brought him, not back then. But the night that your Evelyn, and your mother, crossed, I saw him. Clinging to you and not letting go. I tried to focus on his beauty, but all I could feel was that tremendous, tugging agony of loss. You understand, don't you, Gemma? But for me, there was no appeasement, no goodbye embrace or poignant last words. I had nothing. All I had was a touch, a fingertip's worth of her skin. Her warm, glowing, alive and dead skin. Interesting, isn't it, how we always think of our grief as the worst?"

I cannot speak. She is deep inside my mind, my memories, opening drawers and shaking out skeletons. Trying them on. She looks so beautiful.

"No. I cannot get to your world. I cannot even imagine it. Tell me, is it so different to this one?"

There is nothing. Felicity will not speak. She has been silenced. I never thought it could be done, but I am not glad. I want my Felicity back, the old Felicity that wrapped me up in the forbidden. Not this new, unsure, fractured Felicity.

"No. It's not. It's very similar. Except without the magic."

"Thank you, Ann. I have waited a long time to know that." She inclines her head. Ann does the same. It looks as though she is mocking her. It is dangerous.

"Anyway ... yes, I got a lot of enjoyment watching you and Evelyn talk. Gemma. I am talking to you. You are listening, aren't you?"

This creature is like a child. She is nothing more than a child. Petulant, almost, desperate for your full attention, desperate to know that there is nothing else in the world but herself. But she has been here for hundreds of years. She must know more than anyone, that there is so much else. So much that is more important than us. We are women.

"Yes, she used to give you all sorts of cryptic messages. Warnings. It was amusing. Well, I laughed, certainly. She told you lies, too, Gemma. Yes, imagine that! Lies from the mouth of your dear sister Evelyn. She told you she sent the locket back, with her last remnants of magic. What lies, Gemma, but they were beautiful lies. She found out, of course she did. Younger than you. She found out that it flowed in her, in her veins. She did not need a precious locket. She sent it back to India in that letter she told you about. That, at least, was truth."

The truth stings. It always has done.

"And she tried to warn you about it, did she not? Don't lay your trust in pretty things, Gemma. But you got it wrong, did you not? You got it so very wrong. So painfully wrong. Mistakes, Gemma. They are all you are built on."

The truth stings. It always has done.