a/n: This is sort of an experiment. I love Doctor Who but I feel like I might be rubbish at writing it, so here's a crossover instead? I dunno, I just really like the idea of Lily Luna and the Doctor, and I know he's really in love with his TARDIS, but I just couldn't resist. Enjoy?

Disclaimers: I just thought of a world in which I was creative enough to own either Doctor Who or Harry Potter and laughed. Also: I don't own "Collide" by Howie Day. I do own any mistakes, as there are bound to be some.

–

'tangled up in you'

'Even the best fall down sometimes; even the stars refuse to shine.

Out of the back you fall in time.

I somehow find you and I collide.'

–

one.

Lily Luna has always been quite a handful compared to her brothers and cousins, even with a family the size of the Weasleys she still manages to be the biggest headache of the younger generation. Of course, her mum and dad really should have seen it coming years before the sorting hat placed her into Slytherin. She'd been playing tricks on Albus and Rose since she could walk and no one was a better liar than Little Lily Luna.

Being the daughter of Harry Potter sucks the majority of the time, because people expect her to be as brave and heroic as her parents, but really she's contented with James being the brave one and Al being the smart one. It leaves a nice little gap where she can just be Lily for five seconds without someone asking what she's going to do with her life now that she's an adult.

Yes, Lily has always marched to the beat of her own drum and she quite likes it that way.

It's not a surprise, then, when the blue box falls out of the sky and into her backyard in the middle of the night. Her footsteps are light and quick as she hurries into the back garden, sure that she's either simply hallucinating or mad, probably both. Naturally, she doesn't expect the man that comes stumbling out of it.

"Who the fuck are you?" She asks, more perturbed by the fact that her garden's just been ruined than the strange man now pacing in front of her.

The strange man whips around, as if he's just noticed that she's standing there in her pajamas, staring at him like he's got two heads. "Me? I'm the Doctor!" He says brightly, pushing past her to examine where he's landed, but Lily isn't sure if he's joking or mad. "And that's quite a mouth you've got."

"Like a muggle doctor?" Her eyebrow raises in typical Lily fashion but her words barely register with him before he answers.

"Like the Doctor." He mutters half heartedly, like he's had to say this countless times, before straightening up from his previous crouching position. "Now who are you?" He asks, looking at her flaming hair and blue eyes with a curious expression. She feels like some sort of experiment under his intense gaze and wishes he'd look away.

"Lily Luna Potter." She says, dreading the reaction that always stems from this pronouncement, but instead the Doctor just smiles down at her.

"Lily Luna," He echoes, nodding with the far off look in his eyes he'd worn moments ago, "That's quite a lovely name, yes indeed." He murmurs more to himself than her, before turning back to his blue box.

She wraps an arm around herself before stepping closer to him, "No offense, but you're acting like a total creep right now." She states bluntly, her practically non existent filter slipping, but he doesn't seem too affected by her words. On the contrary, he just continues smiling at her.

"Well, Lily Luna, I am sorry about your rose bushes." He looks down at the crumpled plants, "But for some reason the TARDIS has brought me here."

Lily has no idea what a TARDIS is or why this man claimed he had just shown up in a muggle police box, but she didn't get to ask him more questions before his eyebrows suddenly scrunch together and he moves closer to her.

"What's a muggle?" His question knocks her off balance because he seems to run about a million miles an hour, all in different directions.

For the first time, Lily begins to doubt that this man is a wizard at all. "You know, someone who's non-magical." She says quietly, looking up at him with interest.

He gasps in surprise and what seems to be genuine delight. "You're a witch!" He cheers, putting his hands on her shoulders, which is much too close for Lily. "Well, this is excellent. You're much prettier than the last witch I met." He grins and she decides then and there that he is a mad man.

"Tell me, Lily Luna, would you like to see the stars?" He asks impulsively and she can't even wrap her mind around what he's saying.

She's not sure if he knows that she's spent the past fifteen years of her life looking up at the night sky, falling more and more in love with the stars and everything space had to offer her. She's not sure if he's asking because he knows how lonely she's been because no one has really ever understood her. She's not even sure if he's real, but Lily's biggest weakness is her own curiosity.

Before she can fully realize what she's doing, her head is nodding and he's wrapped her hand in his own, pulling her into the blue box and really, that's when she should have known her life would never be just hers ever again.

–

two.

The Doctor, she's learned, is not anything she would have expected of a man who could travel through all time and space. Mostly he's always smiling and acting like a small child, but sometimes when he thinks she isn't watching, his face falls and he looks incredibly old, which seems impossible. Lily watches him constantly, as she's not sure she'll ever get tired of looking at him. She's only been with him a month and she can count the flecks in his eyes and knows what each smile he gives her means.

There's something he isn't telling her, but even without really knowing this strange person, she's never felt more connected to anyone in her life.

"You're alone, aren't you?" She voices one day when they're lounging on a particularly nice planet in the future.

His face falls for a moment before he glances over at her, an expression she's never seen him wear before gracing his features. "Yes." He says simply, because he's not really sure how to tell her the amount of guilt he carries with him every day or the hate he feels for himself and the fact that he's letting himself ruin yet another person.

She slides her hand into his own and squeezes, "Well, I think you're all right." She smiles and he laughs at her comment, before looking back out into space.

Her heart does the irritating thing it sometimes did when he smiled at her, she felt it skip a beat and she drops her gaze from him. Lily's never really believed in destiny or fate or any of that bollocks, but as she admires the stars next to this wonderful and beautiful and lonely man, she thinks maybe this was the plan all along.

–

three.

It's her sixth time saving the world when she realizes she's been gone from home for over half a year and though she's always been lonely, there are people who have no idea where she's been or what she's done. To be fair, she thinks about them often, usually at night when she's supposed to be asleep and the Doctor is doing whatever mad thing he enjoys late at night.

She sees a little girl on the street, her hair bright pink, following along behind a woman who is thoroughly recognizable. She's supposed to be waiting for the Doctor's signal, but time seems to freeze as Lily watches her cousin stroll along, the small child giggling up at her mother. She realizes with a pang how much she's missed.

Victoire doesn't notice her, but Lily doesn't stop thinking about all the things that could have happened since she had been so foolish and climbed into the TARDIS with the Doctor, deciding nothing was more important than seeing the universe.

It takes a while for her to build up the ability to voice her desire to return home for a bit, because the Doctor is constantly smiling at her, his green eyes bright and full of hope. Lily knows why her chest constricts at the thought of leaving him, and how stupid she's been for letting her heart override her mind for the first time in her life.

He's more than just some mad man to her now, more accurately, he's her mad man, though she'll never tell him this because he's never so much as expressed any interest in her. Why should he? She's going to grow old and grey and he'll still be young and beautiful. She'd just be one more thing for him to lose and she just can't do that to him.

"Doctor?" She cautiously begins, finding him reading a very large and dusty tome in the library. He looks up at her, a child like innocence underlining his expression.

"I was just wondering if it would possible for me to visit my family over the hols?" She feels guilty when his face falls a little, though she doesn't realize he's thinking of another girl with flaming hair and fiery spirit, because maybe Lily and Amy really didn't have much in common, but it would hurt just as terribly to lose Lily as it did with Amy.

"I mean, I don't want to stay for good, but my parents don't really know where I've been over the past six months and I can only imagine the fuckload of trouble I'm in." She says quickly, trying to get him to understand what she really means: I pick you and I'm always going to pick you. But Lily is rubbish at being sentimental so it comes out slightly different.

He's on his feet in the clumsy way that never fails to warm her icy heart and he's nodding quickly making his way to the console. He grabs her cold fingers at the last moment and drags her along behind him.

"Yes, well as tomorrow is Christmas, I think it's best we're on our way now, isn't it?" He says, pulling levers and pushing buttons, (Lily swears half of them don't really do anything but she's had too many lectures to voice her opinion again), before clapping his hands together and smiling to her, because he's so used to her foul language he doesn't even bother anymore.

They reach her home more quickly than she would have liked, considering her mum is probably going to kill her or cry or both and her dad will be the silent sufferer. She's standing at the door to the TARDIS, trying to compel her arm to reach out and open it, but she can't. She can't just leave this world she's come to call home or the man who's finally shown her what true love is.

"Come now, Lily Luna, I'll be back soon." The Doctor whispers from behind her, his hand placed on her small shoulder. "You can't get rid of me that easily." He says with a wink, but Lily doesn't feel like laughing, in fact she feels like sobbing.

"I'm afraid you'll disappear." She admits in a quiet tone, the tears making their way into her bright eyes, but as always, the Doctor knows exactly what she needs to hear. He places his palms on her face, cradling her head in his large hands.

"I would never leave without saying goodbye to you." He promises gently, smiling in a way that momentarily reminds her of her father. "Besides, if you start crying now you'll be all splotchy and look dreadful." He grins and she rolls her eyes before throwing her arms around him, hugging him fiercely.

He waits until she's safely in her mother's arms before he allows himself to retreat into his blue box, a single tear spilling over his nose, and decides he needs to clear his head anyway.

–

four.

Her parents react just as she's expected, with tears and hugs and anger, but mostly they've come to expect Lily's flighty moments. Her father pulls her into his arms and for the first time in her life she feels horrible for how she's treated him. She knows what happened in the war and how much he lost and she thinks it probably wouldn't have killed her to leave a note.

Albus is the first of her siblings she runs into in the warm kitchen, his green eyes bulging slightly behind the glasses slipping down his nose. Everyone in her family knows Lily's really not big on touching in general but he can't help the arms that fly around her and she doesn't really mind.

"Where have you been?" He practically yells at her and Lily just laughs because Al has always been the anxious child, afraid of everything. She strokes his dark hair from his face and smiles at the Ravenclaw boy.

"You wouldn't believe me if I told you." She says, pulling back from him because thinking about where she's been makes her heart ache for the TARDIS and the Doctor.

"Oh Merlin, you haven't gotten married have you?" Albus accuses, sensing something that she's hiding, but in typical fashion, she scoffs and punches him in the shoulder because everyone on earth knows Lily never wants to get married or have children.

She hates the idea of her children being constantly followed by the media. No, she's known for a long time she'll never be a mother, and frankly, she'd be a rubbish one anyway.

"But there is a boy?" Albus asks, and he's always been able to tell these things about her, she thinks that's probably why he ended up in Ravenclaw. The idea that sweet, nervous Al would end up in Slytherin was laughable now.

"It's... complicated." She breathes, before she's cut off by a heard of red hair and adults flooding her home.

She gives cryptic answers to anyone who asks where she's been, but for the most part there aren't too many questions. Running away from home isn't the worst thing she's ever done, but even in the sea of her family she thinks of the stars and the only person she'll ever be able to share that with.

Every night that she falls asleep alone she wonders where the Doctor is and if he misses her at all but if she could see him she would've known that he misses her more than he'll ever be able to express.

–

five.

She was nineteen when the Doctor dropped her back at her home and before she knows what's happened, she's twenty-three and she's convinced herself he isn't coming back. Lily's never been one for relying on anyone else, she rarely has faith in anything, so it makes sense that he won't come back. Rule number one exists for a reason, after all.

It doesn't take her long to figure out what to do with her life, and everyone thinks she's mad for working in a muggle book shop, but the customers remind her of him and she isn't really Ministry of Magic material. She's always been pretty happy with not being anything more than Lily, so she doesn't really care what anyone thinks about it.

"Oy, Potter, there's a customer who needs help out front!" Her boss calls to her position in the back room, rolling her eyes she makes her way into the front of the shop.

Her feet skid to a halt before her brain can register the bow tie and dark hair, because she knows the tall man standing in front of her, not looking a day older than the last time she's seen him. His face breaks into a wide grin when he spots her, moving towards her quickly.

"Lily Luna!" He says brightly before she raises a shaking hand and promptly slaps him across the face. She can't believe the nerve of him to show up five years later and act like it's only been a few days.

Rubbing his cheek gently he scrunches his eyebrows together, "Oh dear, perhaps we should take this outside..." He mutters, gesturing to the door and she can make out the police box on the other side of the street.

She follows him out of the shop, her heart thudding and mind racing, not knowing how to feel about this at all. Over five years she had convinced herself that she hated him, but as the Doctor stands in front of her, cheek reddening by the second, all she can think about are his hands and lips and stupid face.

"I realize I'm slightly late-" He starts gently, stepping back a bit just in case she decides to hit him again, "But there was an issue with an alternate reality and I only just got out-" He's rambling like he always does when he's nervous, she realizes, and it makes her smile involuntarily.

Lily Luna Potter is not one for long declarations or overly sentimental speeches, so she cuts to the chase quickly by flinging her arms around him and pushing her lips against his, not giving him a chance to say anything more. It takes a few seconds for her to realize that he's kissing her back, his long frame holding her close, mouth warm and soft.

She pulls away after what feels like at least four lifetimes, but that could possibly just a by-product of kissing a Time Lord.

"Well, I'm not near as rusty as I thought!" He grins, a goofy look taking over his face and she can't help but giggle at him, because she feels the same high.

"I love you." She says after their laughter has subsided, "I love your stupid bow tie and silly catch phrases, I love your library and how you can make me feel." She says quickly, but he just strokes her face gently.

"I'm just a mad man with a box." He says quietly, a soft smile turning the corners of his mouth up.

Lily just smiles back up at him, "I've never really had a problem with madness, if you hadn't noticed."

"No, I do love that about you." He whispers, leaning into her small frame, his lips meeting her forehead.

"I missed you terribly." He admits and isn't the slightest bit surprised to feel her lips covering his again because for the first time in a very long time, the Doctor feels completely and purely infinite.