Judging by the decorations still adorning the buildings and the trees still shining through windows, it was either just before Christmas or just after.

He knew he should probably figure out what date it was because this wouldn't work if she found the photos before they had had talked about it, but he also knew that he was a scary handsome genius from space and if a paradox happened, he would sort it out later.

He climbed the stairs up to the flat. If he had timed it right, then neither Moira nor Bill should be there. He would have ample opportunity to slip the box somewhere inconspicuous and get out without getting caught.

It was times like these that he understood why Ian Fleming had been so keen to base his Bond stories off of him (and him specifically. Bowtie didn't get to claim that.)

The Doctor reached the landing and made his way down the corridor to the correct door. He raised a hand, planning to knock gently to be sure no one was home before getting out the sonic.

But as soon as he rapped once, the door flung open.

A white woman with brown hair seemingly piled on top of her head wrestled her purse over one shoulder while held her cell phone to her ear with the other.

"Oh good. You're early," she said, relieved. She took the phone from where it rested and held it up to her ear. "No, not you. I'm talking to - Oh, I don't have time for this."

She pulled the phone away and held it to her chest.

"Sorry 'bout that," she said exasperatedly. "She's already in bed, so just be quiet. Phone numbers are on the fridge. You shouldn't need 'em. I won't be gone too long."

Before the Doctor could even consider what he was going to say next, he had somehow switched places with the woman he was only now realizing was the Moira he had heard so much (complaining) about.

"See ya later!" she called behind her, waving at the Doctor as she walked away. "No, not you. I'll see you soon. Yes, I'm on my way."

Her voice cut off as the door closed.

The Doctor blinked.

That certainly wasn't what he expected. But it had gotten him in the door, so he might as well continue on.

He began scanning the house (with his eyes, not his sonic) to find a good hiding place. As he did so, he glanced at the date on a newspaper left on the front table: 27 December .

Perfect.

He decided on a cupboard in a corner of the living room. It was used mostly for storage, given how many plastic tubs and moving boxes he had to shift out of his way to reach the top shelf. But just as he cleared enough space to put the shoebox, he heard the distinct click of a light switch and the cupboard filled with light.

"Who are you?"

That was never a good question to hear.

The Doctor closed his eyes, cursing under his breath. Shuffling the boxes with his foot, he turned expecting to see a sleepy, cross Bill.

Instead, he saw a little girl.

Her skin was light brown and her black hair was pulled up on top of her head. She wore light blue pyjamas adorned with little rainbows and was hugging a brown stuffed bear for dear life. But it was her wide and soulful eyes boring into him that made him realize he had seen exactly what he expected: a sleepy, cross Bill.

Just… a far younger one than he had anticipated.

It was at that moment that he had wished he'd read the rest of the date on the newspaper. Perhaps then, he'd have seen it 27 December 2001 instead of 27 December 2016.

"Who are you?" seven-year-old Bill repeated again.

"Uh… well…"

"Are you my babysitter?" she asked, her little eyes narrowing.

"Yes, yes. That is… exactly what I am," the Doctor said, nodding.

To his dismay, this only made her eyes narrow further.

"You don't look like my normal babysitter."

"Yes, well, I'm a replacement," the Doctor responded quickly. "A substitute babysitter."

They stared at each other for a moment, before little Bill seemed to accept his words as true. He watched as she looked him up and down for a moment before moving her attention to the boxes on the floor.

"Why is all my stuff out?"

But before the Doctor could come up with a feasible lie, young Bill's eyes grew wide with fear. The bear dropped from her hands.

"You're not a babysitter. You're here to take me away!" she cried out. "She said I wouldn't have to go anymore. She lied! She said I wouldn't have to anymore- she promised!"

Tears began to stream out of the little girl's eyes.

"She promised," Bill repeated. "She promised I wouldn't have to move again. She PROMISED!"

The Doctor looked around frantically, trying to figure out why she was so upset when he saw the scribbled out postcodes written on the boxes at his feet. There were at least three marked out on each and underneath each marks was a name: Billie Potts.

"Oh," he sighed quietly in realization. "Oh."

Immediately, he knelt down in front of Billie, sweeping the bear up and offering it to her as he did so. She refused it, her little arms crossed tightly across her chest as she turned away from him.

"I'm not here to take you away," he informed her in the most serious yet reassuring tone he could muster. "I promise. I promise I am not here to take you away."

"Then… why… are...you… in... the... cupboard?" she choked out in between sobs.

"Because I'm a bad houseguest!" the Doctor said. "I'm rifling through your cupboard because I'm rude! I just like to make messes! That's why. It's just… It's just me being rude."

He offered her the bear again, which she again refused. It took every ounce of his willpower to keep himself calm to comfort her instead of stalking his way back to the TARDIS to go make someone, possibly multiple someones', lives a living hell.

"I promise you," he breathed. "I promise you, Bill Potts, I am not here to take you away. I promise."

She must have understood the sincerity of the words because this time, she took the bear from him. The moment she took it from him, she hugged it to her chest so tightly it seemed as if she feared he was going to try and take it from her.

"That's it," the Doctor reassured gently. "You're going to stay here for a good long time, Bill. I promise you that."

Bill - Billie - sniffed again. She rubbed her eyes with the sleeve of her shirt.

"You… you promise?"

"I absolutely promise," the Doctor said, nodding. "I absolutely promise."

Billie took a few deep breaths. For a moment, her gaze lingered on the boxes again before it traveled up to the now-empty space in the cupboard he had made.

"What are you (hic) really doing in the (hic) cupboard?" Billie asked, hiccuping as she looked back to him.

"I'm… well, I'm a, uh, a secret agent. A spy," he said. "And I'm here to complete my mission. Which is to deliver this parcel."

He pulled the box of photographs out of his pocket.

"How did that fit in your pocket?" she asked, her eyes widening as he held it up in front of her. "Are you magic?"

"...Yes," the Doctor replied slowly. "Yes. I am a magical secret agent... babysitter."

"Really?" Billie asked in a slightly teasing tone. "Are you really?"

The Doctor pulled the psychic paper out of his pocket and held it up. She read it, looked at him, and then squinted at the psychic paper again.

"That doesn't look like you."

The Doctor frowned and turned the paper around to look at it.

Sure enough, the man in the photo was not his current face. The one in the photo had blonde curly hair instead of grey and his coat was colorful as opposed to his current black one.

"It's an old photo."

"But it doesn't look anything like you."

"Like I said," the Doctor tucked the psychic paper away. "It's an old photo."

With the psychic paper away, Billie's attention turned back to the box in his hands. The Doctor could tell by her focused frown she really wanted to take the lid off to see what was inside, but she made no effort to.

"It looks like a shoebox."

"Yes. That is what it looks like, isn't it? " the Doctor chuckled, rising to his feet "You are very observant, Miss Potts. But what you should be is in bed. Off you go."

"But I'm not tired."

"Well, how about this then," the Doctor said. "If you go to bed, I'll show you another magic trick."

Billie's eye lit up and she immediately turned and ran off towards her bedroom. The Doctor followed her, still chuckling as he fished something out of his jacket pocket.

When he reached her bedroom, he found her in her place. She sat with her knees pulled up to her chin. Her eyes were bright and attentive, a look he knew quite well from his tutoring sessions with the adult Bill.

"Okay," he began, taking a seat on the edge of her bed. "Do you see this?"

He held up a small bauble and Billie nodded.

It looked like a ball bearing, but in reality was a little device that could create a perception filter. He carried it around in case of emergency and showing up to the right place in the wrong year typically counted as an emergency. He slid the device into the box without letting her see the box's contents and pulled his sonic from his jacket.

"Now, I tap it with my magic wand…"

He pointed the screwdriver at the box. It whirred as he set the filter to be active for exactly fifteen years from that day. Once set, the filter went on and the shoebox "disappeared" from view.

"And… presto."

"Whoa," Billie said softly. "It's… gone…"

"Or is it?" the Doctor asked, smiling.

He pointed the screwdriver again and a moment later the filter went off and the shoebox "reappeared".

"That's so cool," Billie whispered in wonder.

"So," the Doctor said. "You've seen the magic trick. Now you need to go to sleep."

"Can you at least tell me a bedtime story first?" Billie pleaded. "Just one?"

The Doctor considered it for a moment and then gave in with a sigh.

"Alright. Fine," he muttered. He paused for a moment, and then continued, louder this time. "Once upon a time there was a… mermaid. And this mermaid lived in the…"

After a pause to think that lasted a little too long, Billie chimed in.

"The ocean?"

"Yes, the ocean," the Doctor agreed, nodding. "The mermaid lived in the ocean. She was a very nice mermaid. And she, uh, well… she liked to watch the… the, uh…"

"People?"

"Yes, yes. The people. She liked to watch the, uh, people."

Billie narrowed her eyes.

"You're not very good at this."

"I am very good at this, thank you," the Doctor replied. "It's just been a while. Hush. Now...where was I?"

The Doctor took a second to figure out where he was in the story. Billie thought his eyebrows looked so silly furrowed like that that it made her laugh. He raised one at her, which only made her laugh more.

"If you're going to laugh, you don't get to hear the end of the story," he said, his voice serious but his eyebrows wiggling even more.

Billie covered her mouth in her hands but continued to laugh.

"Anyways… there was a mermaid who lived in the ocean and liked to watch the people," the Doctor summarized. "And one day there was a… a nice prince who walked down the shore and saw the mermaid."

But as soon as he added the next line of the story, it felt wrong.

He looked at Billie, who was still smiling, her eyes still attentive as she listened closely to the story. It was then that he noticed the rainbows on her pyjamas and figured out why it felt wrong.

"No, no,no. Not a prince," he said, waving the previous sentence away. "A princess. Yes, there was a nice princess who walked down the shore and saw the mermaid. And she thought the mermaid was, uh, very pretty. And she went into the water to meet the mermaid and then she and the mermaid fell in love and kissed and then… lived happily ever after. The end."

It was Billie's brow's turn to furrow. She tilted her head to one side.

"Was the princess a girl?"

"Yes."

"Was the mermaid also a girl?"

"Yes."

The Doctor watched as the little girl contemplated this.

"Can… can girls kiss other girls?"

"Yes, they can."

But Billie suddenly looked very concerned.

"But is that allowed?" she whispered nervously, like if she asked the question out loud someone was going to hear and get mad at her.

The Doctor leaned forward and looked her right in the eye.

"Yes, it is. And if anyone ever tells you it's not, then you come and find me. I'll put them right," he said seriously. Then he gave her a small smile. "But something tells me, Miss Potts, that you are going to be very good at doing that yourself."

Billie beamed, which earned her a sincere smile from her magical secret agent (alien) babysitter.

The Doctor rose from the bed as Billie shuffled underneath her covers. He flipped the light switch just as a small voice bade him goodnight. He returned the goodnight and closed the door softly behind him.

Within minutes, he had turned the perception filter back on and hid the shoebox full of photos in the cupboard. He put all the moving boxes back in the cupboard, figuring that reducing them to cinders was probably frowned upon within estate grounds.

He returned to the kitchen only to hear a knock on the front door.

He opened it to find a very confused teenage girl standing in front of him.

"Ah. You must be the babysitter." The girl could barely eke out a "yes" before the Doctor stepped past her. "She's already in bed, so just be quiet. Phone numbers are on the fridge, but you probably won't need them. She'll be back soon."

When the TARDIS touched down back in his office, the Doctor wondered briefly if Moira ever noticed that the babysitter she had greeted was not the same when she returned.

But before he could wonder that for too long, he heard footsteps down the corridor.

Expecting it was Nardole coming to give him a stern talking to, he gathered up a bunch of large, old papers that he needed to file.

"Happy new term!" he heard Bill, adult Bill, greet happily.

"With you in a moment," he said quickly, rushing the papers into the back room even though it was not the visitor he had expected.

Bill waited patiently for him to return, only to notice the strange blue phone box was now sitting atop the rug she had given the Doctor for Christmas.

"You said you needed a crane to lift your box," Bill stated, eyeing it suspiciously.

"Sorry, what did you say?" he called from the other room.

He stepped out a moment later.

"I didn't hear you. What did you say?" he repeated, making his way behind his desk.

"I just thought…" She looked from the phone box back to him and then shook her head. "Nothing. Nevermind. Anyways, did you have a good Christmas?"

"Uh… Yes. Yes, I did," he said, making a mental note that apparently he had skipped Christmas this year. "You?"

"Yeah. It was pretty normal," Bill shrugged. But then her eyes lit up. "But there was this one thing. It was… Okay, so you know how I told you that I didn't have any photos of my mum?"

"Yes, I do recall you saying… something like that."

"Well, the other day my foster mum was cleaning and she found an entire box of them in the cupboard. An entire box, like a shoebox full, just of photos of my mum."

Bill positively beamed at the thought, the reality, that such a thing existed. She was still smiling a moment later when she rubbed tears from her eyes.

"Are you okay?" the Doctor asked, concerned.

"Yeah, yeah. Sorry," she apologized, chuckling slightly. "I'm still like crying about it. It's just… We had no idea they were even there. I… It's just incredible. Like… a Christmas miracle. Seriously. It's pretty amazing."

Bill continued to chuckle through her tears. The Doctor was not entirely convinced that she was alright, but wasn't sure what to do next.

"Uh. I'm glad. About… this. I'm… happy for you," the Doctor said slowly, clearing his throat. "Glad you had a good Christmas."

Bill smiled happily at him for a moment and then glanced at the clock on the wall.

"I gotta get back," she sighed. "I just wanted to stop in and say hi."

The Doctor frowned.

"You mean it's not six?"

Bill looked at the Doctor like he was, well, an alien.

"Umm… no?" she asked confusedly. "It's lunch time."

"Right, right," the Doctor nodded. "On…"

"January... 9th?" Bill said slowly. Her eyes narrowed. "Are… you okay?"

"Of course," the Doctor said with a shrug. "It was a test. A… time test. Which you passed."

Bill's brow furrowed.

"Oooookay," Bill chuckled suspiciously. "I'll see you later."

"Yes. Later."

Bill turned back to the door. The Doctor watched her go, but before she stepped into the corridor, she hesitated.

She turned back for a moment, her mouth open as if to say something. But then she shook her head and turned back towards the corridor.

"Is something wrong?"

Bill spun on her heel to face him.

"No, it's just…" Bill took a deep breath. "In one of the photos… it looked like, well… you."

"Me?" the Doctor asked, feigning confused curiosity. "I thought you said they were photos of your mum."

"Well, yeah," Bill admitted. "They are. But in one of them there's like this reflection. And it sort of looks like you. Like you're taking the photo."

The Doctor waited for Bill to either make the accusation, make the connection, do both, or ask a follow-up question. Instead she just laughed and shook her head at what she perceived as her own imagination.

"It couldn't be you. Must just be some bloke that looks like you. But I doubt there are many of them around," she smiled. "Anyway, I'll be back tonight. Laters."

She waved at the Doctor and turned to the door one more time. As she stepped out of the door into the corridor, she heard the Doctor's unmistakable Scottish voice mutter something that she pondered all the way back to the canteen. Something strange yet oddly familiar.

"Could always be your magical secret agent babysitter."