"Police in Oregon are seeking leads in the mysterious disappearance of Olympic hopeful Jessica Burroughs, who vanished from her family home only weeks before selections for the national swim team last month. At first, the authorities had surmised Burroughs had left of her own volition – perhaps feeling pressure for the upcoming trials. However, Burroughs' distraught parents have always insisted their daughter would not have left of her own free will without a word, and today, they came forward with a message they had received from – we surmise – the swimmer's kidnappers."

I sat there on the sofa, frozen from the first mention of Jessie's name, her face superimposed onto the screen – a smiling High School Yearbook picture, a heartbreakingly familiar stranger. And then I stiffened as the feature interview began, a sympathetic, shiny-haired newsreader holding out a microphone to a gaunt couple I recognized all too well.

My father hadn't changed much at all – just as I remembered him, he was slope-shouldered, awkward-looking, a big man trying to make himself unseen. He had always been a background presence, remote and unreachable, lacking colour. My mother had always taken the lead, and this remained the case even after all of these years, leaning forward to stare into the camera with her harrowed, red-rimmed eyes. The kind newsreader visibly leant away from her, as if her naked grief might be contagious.

"Mrs Burroughs, can you tell us what the letter you have received demands? Is it a ransom note? Do they make threats?"

My mother didn't even look at her. Her eyes remained fixed on the camera. I felt a sudden disconcerting certainty that she could see right through the TV screen to where I sat, safe and warm in a stately home while her other daughter – her real daughter – was God knows where. I felt an irrational stab of shame. She began reading from the note she held scrunched in her yellow-knuckled fists.

""You know where she is. You know what I want. You know where I am. I'll be waiting. But I won't wait forever. As you know, my patience has its limits.""

The eyes snapped up back to the camera, and there was a raw, exhausted demanding in them that went beyond a plea. I felt that look right down into my bowels.

The bewildered newscaster tried to get her attention.

"And do you know who it's from? What is it you know they want?"

My mother shook her head.

"The message isn't for us."

Finally, she broke her dreadful gaze, demanded "when will this be broadcast? Where? How many channels? It needs to go out to the whole country, it needs to reach-"

At that point, someone in the control room obviously decided this was all too weird, and cut back to the main newsroom. A slim brunette began to deliver the weather report, oblivious to the fact that my whole world, or what was left of it, had just been swept away as if by a strong wind.

Fiskel. Fiskel had taken my sister. He had taken my sister to get me back.

I don't need to explain this to you, Raven. Anybody else, maybe. But you know what it's like to have a sibling. There's something about that relationship which goes deeper than anything else. I know you'll understand the way I felt, just like I understand that every day you spend without talking to Charles will feel like who you are is sheared away, one wafer thin slice at a time, until you're left with – what?

If nothing else, it puts whatever the hell it is I feel for Erik into perspective. When I heard that he was being held, I was desperate to save him, or so I thought. But without help, without any clear plan, the idea stagnated, became a nagging guilt I could allow to vacillate. I knew, the minute I understood what had happened to Jessie, that wasn't an option in her case. I didn't want to rescue her. I needed it to be done, yesterday. Every minute I didn't know that she was safe was an abomination. And anyway, I could only grimly imagine what was being done to Erik; with Fiskel, I knew all too well exactly what he was capable of.

I almost felt sympathy for that bone-hard, red-eyed woman from whose womb my sister and I had both come. I recognized that howling need in her. Which was exactly what she meant for me to see, the newscast her only way of reaching out to me, her only hope, and insisting that I sacrifice myself to save her child. What else could she do?

I was at Charles's door without even realizing I had meant to go there, entered without knocking. He was sitting at his disordered desk, and thrust a photo-frame guiltily under a pile of papers when I entered.

"Maddy, what do you want? I'm – busy."

I still couldn't get used to him without his powers. He seemed so – hollow, somehow, so remote. I was used to the gentle feeling of his mind reaching out companionably to mine – without it, it felt like he was somehow only half there. But I had no time to feel the usual sadness this usually provoked in me. I explained in as few words as I could what had happened. His face seemed to close up on itself like the shutters of a house as I finished.

"I feared this might happen. I only hoped somehow you wouldn't have to know."

"What do you mean?"

He sighed, pushed the lank, greasy hanks of hair that hung into his eyes off his forehead.

"Before the serum, before – everything – a few times, Fiskel's people tracked you down as far as Westchester."

I stared at him in shock. He continued.

"You know he had people looking for you just after you escaped. I guess you thought that they had given up. But Fiskel's a persistent man, and in any case, he was desperate. You can't make promises of miracle cures to the kind of powerful people he did then fail to deliver. He needed you back. They found you here. I… sent them on their way, with confused minds. Eventually they stopped coming. I'd hoped he'd finally given in, or that perhaps his crimes caught up with him. But there was always the possibility, while he was still alive, that he'd work out you'd found a place to hide from him – that if he wanted to get you back, he'd have to find some way to make you give yourself up of your own free will."

"And now he's found it," I breathed. "Why didn't you tell me all this? Why didn't you warn me?"

He sighed, leant his head on his steepled hands.

"I didn't want you to worry. After all, what could you do? Fiskel would be watching your family. If you made contact with your sister, tried to warn her, he would know where you were. It would be only a matter of time before he tried to capture you, brought down God knows what on this house. I had to try and protect you, and everybody else under this roof, protect the school."

I stared at him, caught between my desire to understand his point of view and a rising red rage that he had taken these choices from me, sacrificed Jessica without her consent or my knowledge for the dream that now lay in rubble around our feet. I took a deep breath, tried to think clearly through the screaming urgency to save her.

"Charles. Listen to me. None of that matters now. What matters is saving her. I need you to help me. You have to help me. You need to use your powers, use Cerebro to find Fiskel, to find out what he's planning, to stop him. I need to know that she's alright!"

I swallowed in my panic, looked at him, was utterly appalled to see he was shaking his head sadly.

"I can't. I can't. I'm so sorry, Maddy. But I just can't. I need the serum. I can't stop. If the voices come back – so many voices, so much pain, I can't control it any more, I just can't-"

I slammed my fists down on the desk.

"What do you mean, you can't? He'll kill her, Charles. My sister!" He stared at me blankly, helplessly, bright blue eyes filmed with tears. I dropped to my knees at his side, more desperate than I had ever been.

"You've done so much for me Charles; please don't think I'm ungrateful. But I've never asked you for anything before. I'm asking you now. You only have the serum because of me. I'm begging you. Please try to help me. Just try. Please!"

He was silent a long time. Even though I knew it was pointless, I broadcast to him my feelings of fear and dread as powerfully as I could. The Charles I knew, the old Charles, with his powers of empathy and compassion, would never have been able to resist my appeal if he could have felt what I was feeling.

But the new Charles, this only human Charles, just looked up and gulped, put his hand over mine and shook his head.

"I'm so sorry, Madeline, but I can't."

I jerked away from him, the betrayal burning like bile down my throat, filling my mouth with words I knew if I spoke them would ring in my head guiltily forever after, would burn whatever rickety bridge still made a path between his heart and mine. I spun around and ran out of his study. He didn't even try to call me back.

You know my memory is faultless; but everything since then, when I look back, is as if it was somebody else, not me. My mind was a total mess; but my body went calmly up to my room; dressed itself in black denim and leather; pushed clothes into a duffle bag; took out the padded envelope under my bed which contained all the documents Erik and Charles had given me so long ago, my passport, my bank accounts, my 'new life'. Ruth Xavier. My body thrust these into the bag too.

I went down to the lab – Hank wasn't there – and drew several phials of my own blood, labeled them precisely and put them in the fridge for him to find. I knew he had managed to replicate the DNA he needed for the serum; but you never know – he might need my mutation for something else, by and by. I didn't want to leave him with nothing. He deserved better than that. In exchange, I took a couple of bags of human blood, packed into a coolbag.

And then I sat down to write you this letter, Raven, to apologise. I let you down, you who I love as much as a sister – but my real sister needs me now, more than your brother, more than anyone.

I'll wait until Hank comes back, then I'll give him this letter to give to you, if you come back. He won't have opened it. You know that whatever else, he's not capable of betrayal. And then I'm going to look for my sister, and try to save her, because no-one else can. I can't trust Fiskel – why would he release her once he's got me? – but at least I have to try.

I hope you can forgive me; and I hope one day I get the chance to forgive Charles, when this hard apple of anger in my chest has withered and softened, when once again I can make allowances for him being only human, for his choosing to be only human. It's an appealing choice; but it's not a choice that I have any more.

Goodbye Raven; thank you for everything you've been to me. I hope you found what you were looking for, and fought the good fight, and stayed the course, and kept your faith. I hope that I will see your face again some day.

Maddy.