cut your body into turquoise pieces

He had rules about these things. Not crossing his own timeline, not revealing the future to him even though he would really want to know.

But then she had her own rules too. The Doctor lied. He bent the rules sometimes, and honestly this wasn't bending so much as tweaking it, just a bit.

She was at a playground, watching a small group of school children scramble over the hovering equipment. One small girl keeps glancing over at her, plucking up the courage to sneak over and approach her. When she finally does, River smiled down at her. At herself – forty years ago.

"Hello River."

The child is startled, pushing her curly red hair out of her face as she looked equal parts intrigued and scared. "How do you know my name?"

"I know lots about you, but I can't tell you how. I know you shouldn't be talking to strangers right now, dear, but I'm not going to hurt you. Do you trust that?" River was very serious as she spoke and the young girl in front of her nodded, moving to sit next to her on the bench. She reached a small hand up to touch River's hair curiously.

"Your hair's like mine. I hate mine. All the girls make fun of it." The little girl sighed gustily and River laughed out loud.

"Never you mind them, darling, hair like ours is a blessing. Someday someone will just absolutely love it. And you." She pulled out an envelope – bright, familiar blue – and handed it to her younger self. "I want you to read this, okay poppet? And I'll send you others for a little bit if you'd like."

"Like a pen pal? Can I write you back?" The girl took the envelope reverently, her small fingers tracing the glued down flap.

"Well, no not exactly. But if you write letters to me, and then put them in your diary – I'll get them, alright?"

"Like magic?"

"A little bit, yeah."

"And I can have a friend. None of those other girls have a pen pal. 'Specially not a grown up one that's pretty, like you." The little girl stared wistfully up at her and River's heart clenched with the memories. She'd hated the girls at her school. Always dressed in pretty little skirts with their hair in perfect ribbons, looking down their noses at her in her baggy pants and her mop of hair.

"The most important part, River, is that you can't tell anyone about this. Not the other girls, not anyone. Not ever." She knew this wouldn't be a difficult secret for her younger self to keep. And honestly, it's not like she'd had many friends at the school growing up. And the home wasn't a place you found friends. She'd spent her formative years with her nose buried in history books, yearning for escape. And by the time she was older – well, she'd know well enough to never ever tell the Doctor.

"I promise." The girl spoke solemnly. "I like the colour of your envelope. It's such a pretty blue."

"It's my favourite colour." River whispered back secretively.

"Then it'll be mine too. Can all of them be this colour?"

"I promise." River answered, wrapping one arm around the girl and squeezing her just a bit. "Now run along, River. And don't read that until you get home. I'll write again soon, alright?" The younger girl nodded, folding the envelope and shoving it into one of her side pockets before taking off at a run, back to the playground. River watched herself run, and sighed.

He wouldn't approve of this, she knew. But it had happened already and he couldn't stop her from making it happen again. She needed to be prepared.

With another soft sigh, she touched the button at her wrist, and disappeared in a cloud of smoke and electricity.

I've always liked a nice bow tie. So old fashioned – did you know they originated on 17th century Earth? One of my favourite time periods, River.

Plus magicians wear bow ties. And I love a good magician.

She kept her childhood diary under her mattress in her cell. She read it less than her current diary, but she loved going back through it and finding letters to herself. Her younger self was inquisitive – always thanked her for her letters, and wrote every entry in cerulean blue crayon.

Blue is my favourite colour because it looks like the sky just after sunset. Getting dark but for just a second it's bright with possibilities.

She sent herself the Tardis blue diary. Mailed it out for her own birthday, popped back a good few years first before putting the wrapped package in the mail and getting back before the guards have even realized she was gone. After that, the entries to herself were inked in the very front of her own, like magic.

Stay on guard always. But you can always tell what sort of a person someone is by looking into their eyes, River. Kind people always have kind eyes. And bad people can never quite fake that quality. Sometimes I can trust complete strangers. Sometimes they're not strangers at all.

She knew he'd find out, one day. One day when she dies, he would get this book, all these pages of her life, bound and wrapped by his blue. He'd know what she did then – but she knows he won't change it. Not one line.

Impossible things happen every day, dear. There is nothing that is truly impossible. I learned that from the best – and now I'm telling it to you. But you already know that, don't you?

The thing is – the thing is it was getting more and more difficult each time she saw him. Each time she looked into his eyes and saw less of the man that loved her. Oh she still sees the man she loves, because she could never not see that when she looked at him – but his love is diminishing, and it hurt in a way she hadn't quite expected. The entire goal of this endeavour is so that he never had to see that look in her young eyes.

You can love someone you've never even met. Sounds impossible doesn't it? Which is why we know it's true.

This was why she knew, that in the afterward, when he goes back through the book of their lives – he won't try to change anything she's done. When he gets to those last entries, raw pain poured out over the pages, he'll know what she spared him from. She liked to imagine he would be thankful. She always was martyring herself out for him. It was a quality he loved and hated about her.

I can only tell you this; live fast, learn everything you can, value yourself. Because one day you will meet a man – a magical man who will be an equal – and he cannot value any more than you do yourself. Love that man, River. Love the possibility of impossible things. Maybe his favourite colour will be blue too.

She sent the last letter three weeks before her younger self is due to meet the Doctor. She laid back in her tiny cell afterward, letting the memories wash over her. She'd loved that box before she even knew what it was – ran her hands over the wooden surface and marvelled at how blue it was.

Always hold his hand when you need to run. Don't ever let go.