Sister,

It's time we made up. I'm so sorry that it has taken this long. I've lost count of all the times I've come to sit by this headstone over the years, in silence. But I lost you, putting it off, and I just don't care that it's too late any more. I just had to tell you that I'm sorry. I'm so sorry.

Remember when we were little, and we'd explore the forest together? Mom would curl my little hand around yours and tell me, 'Look after your little sister. Don't let her out of your sight." Of course, we'd let go of each other as soon as we were hidden by trees, to play hide and seek or to climb or to simply explore. Sometimes I'd lose you on purpose so that I could search in secret for wild lilies to pick and bring to you. I had no idea that your mission was the same until you beat me to the goal, presenting me with a broad smile and an armful of colourful petunias. We thought nothing odd of it at the time. We were too young to know that petunias growing in perfect rows deep in the woods made no sense.

I have to wonder how many little things did escape our notice, because it wasn't until that day you were shouting at me and the candle lit itself in your hand that we realised something strange was following us. It didn't take long to realise that it was you. It was always about fire with us, wasn't it? Right from that candle. I wanted so much to share your power, what I thought was your gift; I tried so hard, but I couldn't light even a match without striking it. So I accepted, once again, my role as your protector. I know that you sometimes felt bad for me, but don't – it was an accustomed role. You were always the special one, the bright little star, the one who drew attention and smiles. I knew that it was my destiny to shield you from fear and disapproval. From finding you in the forest as night fell to killing spiders to taking the blame for something you had done, that's the job of an older sister. And I did it.

I took the blame when your mysterious power left things broken or scorched. I watched that Snape boy follow you around like a hungry puppy, I followed him for a week before pronouncing him harmless. I screamed at Big Marjory's gang when they called you a freak, made a scene before she had a chance to hit you. And then the letter came, that would take you away from me.

I didn't want us to be separated, I told you. You agreed, said you didn't want to be apart from me. I told you to stay at home, come to my school instead, but the lure of magic was just too much for you. Power and mystery meant more to you than I did. You left. Our letters to each other became rarer and rarer, weekly correspondence became monthly. I learned to sew and calculate angles. You learned to make sleeping potions and turn crickets into buttons. You came to home for the holidays, but every time, you and I had grown more in different directions. We were growing apart. It was normal, I suppose, for girls growing up. It still hurt.

I still remember that time that Big Marjory and her girls rounded on us after your first year. "Oh look, the freak's back!" I stood in front of you, ready to shout her down, but your hand was already going to your pocket. There was no fear in your eyes, just the disdainful look of somebody who has reached the end of their tolerance for some minor long-term annoyance. I knew what you were reaching for. I shouted her down quickly, not caring if I attracted a few munches this time; I needed to get you out of there as quickly as possible. It wasn't until we were alone that you took your hand off your wand and I felt safe enough to ask you just what you thought you were doing. "You're not allowed to use magic here!" Your only answer was to glance meaningfully in the direction of the old Snape house and explain, "They wouldn't know it was me." I had the haunting suspicion that getting you alone hadn't made things any safer.

That was the first time that I had ever really been afraid of you. Do you know what that's like, to be afraid of your own sister? To know that you, with that piece of wood, were a single angry impulse from doing whatever you wanted at any moment? I tried to bury the feeling – I knew you, I knew you were gentle, you wouldn't hurt people. But I couldn't forget the way you'd looked at Marjory. I'm sure you weren't going to hurt her, only scare her like she'd scared us so many times when we were little. But I couldn't shake the feeling.

I should've spoken to you right then. I think you would've smiled at me and handed me your wand for the holidays without me even needing to ask, and everything would've been better. Instead I just kept trying to bury the feeling. Our parents loved your magic. You loved you magic. I told myself I was being silly.

I'm so sorry.

But you were only home for a few months at a time at most, and it was easy to ignore. Years passed, and I didn't see you so easer to attack somebody again. I put my fears out of my mind. You came home and introduced me to your James, a passionate if cocky boy who treated you like a princess. I introduced you to my Jason, with adventure in his heart and a desire to show me the whole world. And then the fire happened.

Once again, I shared the price and none of your power. I know you think I blamed you. I didn't mean to. But if you hadn't gone to that school, if you hadn't learned to be stronger, maybe things would not have gotten so out of control. Maybe Jason would have had a chance. Anyway, weren't they supposed to teach you to control your power? To use it safely? But you acted as if you were blameless, as if they were blameless... you took it as a personal insult when I flinched when you reached for you wand. And after I had that shouting match with James, and you stormed out...

When I got to know Vernon, things got better. He understood my desire for a quiet, normal life. He didn't look at me as if I was betraying my family or gender or humankind when I confessed that I wanted to be a regular housewife in a suburban house. I saw nothing wrong with his wish to get a normal office job and rise through the ranks of a big business. "I'll look after you," he promised. "I'll give you everything you ever wanted." We even agreed on kids – "Just one," we said, "so that we can concentrate on giving them all the love in the world, and they'll never want for anything."

I tried to invite you to the wedding. I wrote out the invitation five times. I posted none of them. I knew you didn't like him, after all; the first time you'd met you pulled me aside and hissed "Big Marjory's brother? Really?!" and things hadn't improved since then. I knew that you wouldn't want to come, but you'd feel obligated, and it would be awkward. We didn't come to your wedding for the same reason. You didn't want people like us there. We weren't comfortable around your kind. No need to burden you.

And when Dudley was born... I just had no idea whether your kind even had christenings. I supposed that you mustn't, after your Harry was born, and I had to hear about it from mother. At least you met Dudley, once or twice. I never even met Harry.

Until that... that day, when the whole world came crashing down. I knew your world was dangerous, sister, but evil wizards killing your friends? Secret rebellions against a dictator? Why didn't you tell me any of this? Why did you think you had to do it alone? I couldn't do much to help, I don't have your power, but I would have tried! I had the right to learn of this from something other than a note tucked behind the head of your newly orphaned child, left on my doorstep!

Vernon and I had never wanted a second child. And the last thing we wanted was some terrifying witch-child who could bring the whole house down around us at any moment. But he was family, and I wasn't abandoning him.

"He's going to have it," Vernon had insisted. "No doubt about it."

"I know," I'd replied, "but we have to do our best to protect him from his own power."

"Dudley could be in danger."

"We won't let that happen."

At first, we just kept a close eye on the boy. Perhaps we'd be lucky. Perhaps it skipped a generation. But no; he was barely a toddler when odd things started happening, things that we couldn't ignore. Toys that were locked away appearing in hand. Animals calmly crossing the street to be petted. Each time, we disciplined him; he had to know that his powers were dangerous, that what he was doing could hurt someone. I don't think that you would have approved of the severity, but that's just it; you had a piece of wood that you could wave about to make everything better. We didn't. We were at the mercy of a two-year-old's whims, and as he grew older, he only became more dangerous. And the only thing we could do to protect ourselves, and our son, and our nephew, was to make sure that he used his power as little as possible. We couldn't afford to be lenient.

When Dudley realised what was happening. He started covering for Harry, playing big brother. We couldn't have that either. We put a stop to it.

We did our best to protect your son. We wanted him to grow up in a normal house, we wanted to protect him from the world of magic and from himself. But they wouldn't let go that easily. Eventually, the letter came.

We tried to ignore it. We tried to hide. Eventually, we tried to run; we abandoned our own home, left our life behind, to try to protect him. We hadn't planned for that possibility well enough, but we had planned for it. We'd agreed that if we had to run, if we had to give up our happy, normal lives to protect him... well, we had promised to protect him.

We underestimated how badly your world wanted him.

They sent an enforcer after us. A huge wizard cornered us out in the middle of the ocean and started flinging curses at my son! We tried to keep Harry safe, I swear we did. But please understand, sister, we were doomed from the start. Vernon, who abhors violence, even tried to scare the intruder off with a gun, but when that proved useless and he started attacking our Dudley... there was nothing that we could have done. I couldn't protect your son. I could only try to protect mine.

I didn't have the power to stand up to your kind.

He was entranced by the idea of wonder and sorcery, as you were. Vernon suggested that maybe we'd gone about things all wrong, that maybe we should have spoiled him and tried to make him love the normal world, but our parents had always showered love and affection on you and you'd still run off with the wizards. No, I think we were doomed from the start. It's didn't stop us trying again, though, when he came back after his first year and started bullying Dudley with his powers and sabotaging Vernon's career with floating desserts. We tried to hold onto him. Wizards broke him out. The second year, he physically attacked Marjory, as I has managed to stop you doing all those years ago, and stormed out of the house. When the emergency response crew (at least your kind makes some effort to clean up these dangerous messes) told us he wouldn't be coming back until next holidays, it was somewhat of a relief. He was more aggressive, more impulsive than you, and so much more dangerous. He was impossible to control.

And he brought more danger than simply himself. I wasn't aware of just how much he was risking his own life, that life that you and we had sacrificed so much to preserve, until we were told that we were in danger. That we needed to move. Vernon wasn't happy, but we had been prepared to move for his sake before, all those years ago. It seemed that it was my destiny to pay part of the price for his power, as I always had for yours.

When we left our house behind, I was worried that we were seeing him for the last time, too. It seemed inevitable that the evil that had taken you would also take your son. And we hadn't been able to protect him. Despite all our efforts, we were powerless.

So I bring you these flowers, sister. Lilies, like I'd tried to find for you in the forest all those years ago. They're your son's. Oh, he is not dead – it seems I was wrong about that. Wrong about a lot of things, really. I think... I think that maybe, while it's a guardian's job to protect a child from the world, it isn't their job to protect them from themselves. Harry was stronger than I gave him credit for. Perhaps, given my lack of power to protect him from magic, I should have trusted him to use it wisely. Perhaps I shouldn't have tried to protect either of the boys from absolutely everything.

These flowers are from your little Harry's wedding. I'm sure he'll be along shortly to tell you all about it. He married Genevra Weasley, the daughter of two of your old comrades-in-arms, I believe. She seems to be a clever girl, and I suspect that she can protect him better than I ever could, even sharing his curse. I think your son is going to be okay, Lily, no matter what happens. He can handle anything. I know he can, because when he was trading vows at the altar, I took a long, clear look at his eyes.

He has your fire in them.