There is a strange duality inside her. On the one hand, she is still Emma Swan, with the sum of Emma Swan's experiences. She still likes grilled cheese, cocoa with cinnamon and wearing leather jackets with too-tight jeans. She still loves her son like breathing, and loves his other mother with an ardour that had taken her by surprise when she realised it, and still does. She still has nightmares that everyone she cares about will leave her, just like they always have.

On the other hand, there is a dark and ancient chorus of voices whispering to her. You need never fear again. You are strength and power and all will bow before you. She feels their experiences intimately – memories of violence, bloodshed, power – and over time, the distinction between their experiences and hers is becoming more and more blurred. They whisper such seductive things – you can protect your loves, obliterate any who would stand against them, any who would harm them – and she wonders how long she can resist them, how long it will be before the voices stop being other and start being self.

She had fled Storybrooke in the immediate aftermath, the war of light and dark magic within her threatening to spill out and destroy everything and everyone around her, like the detonation of an atomic bomb. The power had been such that she'd been able to punch through the fabric between worlds, and she'd found a space, a void, where there was nothing, no one she could hurt. She'd stayed there for a time, perhaps minutes, perhaps aeons, until the raging, roiling, energy in her had quieted a little. It still crackled just beneath her skin though, like a thousand tiny electrical storms, the potential for destruction infinite, boundless.

She would have stayed there longer, forever if she could. But she'd felt the pull of the dagger, the sound of her name echoing across the vastness of space and time, and although she'd tried to resist, there was a twisting, tearing, rending sensation, and suddenly she was standing in Storybrooke once more, her mother holding the dagger up to the sun.

Snow's arms are around her, and she's crying, great gasping, gulping sobs that Emma can feel with her whole body. "Emma, Emma. Thank god you're safe." Emma can feel Snow's tears dripping onto her shoulder, soaking her shirt, and there's a queer urge welling up in her to lick them off her face before they fall, taste her pain, swallow it up inside her. The voices are whispering to her again and she tries push them away. She's hurt you before. She'll hurt you again, hurt others. Don't let her hurt anyone again.

There are images flashing behind her eyes, scrambled, almost too quick to comprehend: Snow's heart in her hands, pulverised into dust; Snow with her head at a curious, unnatural angle and flat, lifeless eyes; Snow with eyes and tongue bulging out and Emma's hands wrapped around her throat. Emma stands there like marble, her hands clenched at her sides, as her mother continues to wail.

Eventually Snow steps back and looks at her and Emma can see her flinch a little at what she sees. She hides it well, but not well enough; with her new eyes, Emma can see the energy transfer in a collision of atoms half a universe away. Reading the face of a woman who has never been good at keeping secrets is child's play.

Snow is calmer now, as she speaks. "Why, Emma? Why would you do that? You saved us all, but why would you sacrifice yourself that way?"

Emma is silent, but inside there is a voice that this time she recognises as her own. Not for you. For her. Everything for her.

Snow carries the dagger at all times, and Emma feels it as a leash, both welcome and chafing. Under Snow's control, her hands are still clean, but her soul is still being tarnished gradually with generations of destruction.

At first, Snow tries to insist that she live in the town, with them, but Emma looks at her with dead eyes, and watches as Snow shivers. "I could end everyone in this town with a thought," she says, and Snow agrees to let her live in the forest, commands her, in the end. And so, Emma is tied to a cabin in the forest, not allowed to take more than a hundred steps from its door, waiting until they find a way to bring her back to herself.

Killian comes to see her, and he is like a shattered mirror, all she can see in him is herself, distorted and strange, from a thousand different angles. She can smell him before he even walks into the room, his body reeking of the sour smell of rum and desperation.

He moans and sobs and swears, and she watches as the knuckles of his one good hand become swollen and bloody and mangled as he punches the wall again and again and again.

"Swan, why'd you do it?"

She sighs, and a moment of gentle affection for him unaccountably wells up, before quickly being quashed again. "I couldn't not do it." The voices whisper again. He's a fool. Unworthy of you. Crush him for his insolence, his presumptuousness.

He looks at her with such anguish, his pretty blue eyes bloodshot and wounded. "You made me want to be a better man, made me want to turn my back on darkness. But I'm not enough for you, am I, never was."

She remembers telling him she loved him. She'd lied, a kindness to make him feel better, but looking at him now, she thinks that it wasn't a kindness at all.

"Did you ever love me, Emma?"

Her eyes are hard and her voice is harder. "No."

He leaves Storybrooke that night and she's glad, because even though she never loved him the way that he loves her, she still cares enough to be relieved that he won't be in her line of fire anymore.

She refuses to see Henry, terrified of what she might see in his eyes, unsure whether hope or fear would be more devastating. Snow tries to keep him away, but Henry, sweet Henry, is as determined and resourceful as ever.

She feels him approaching, and she hides, folding light and shadow around her until she is no longer visible to his mortal eyes. He stands there, searching, calling for her. "I know you're here, where are you?"

Seeing him is like a small tendril of sunlight sneaking through the clouds in the depths of winter, and she allows herself to enjoy it for a moment. She ignores his calls, screwing her eyes shut and clenching the muscles in her jaw. The urge to hold him, to ruffle his hair is almost overwhelming, but she knows it's not safe, she's not safe.

And then he pulls the dagger out, and Emma knows a moment of horror, before she's torn from the shadows.

"Emma Swan. Dark One, I summon thee."

She groans, "Henry, what have you done?"

He's crying, and Emma reaches out and traces the path of a tear down his face, the face that is not quite that of a boy and not yet that of a man. He shouldn't have to endure this. The voices are there again. You can keep him safe. So many have hurt him. Lay waste to them all.

"I need you. Mom needs you. She's not been the same since you did this. She's broken." He looks at her with hope in his eyes. "I need you to put her back together again. Come home."

Emma can feel her breath coming quickly, and it wells up in her throat until she's screaming. She can feel the magic pulsating under her skin, feel the rage building, molten metal burning through bone and muscle and skin.

Henry is cowering in front of her, and this is what brings her back to herself. She looks around, and realises that the cabin is no longer there, and nor are any of the trees for at least fifty yards. There's only destruction. And for the first time since she'd taken on the darkness, she feels moisture in her eyes, and a solitary tear tracks down her face.

It was all for her, for nothing. Regina.