Clara stepped out of the Tardis, the welcoming creak of the door echoing through the wide room of sandy stone walls. The Doctor quickly followed, frowning down at her as he did so.

"Hey, you can't do that," he huffed, adjusting the lapels of his cashmere cloak.

Clara turned to him with poised eyebrows. "Do what?"
"Well, you know…" he fidgeted, momentarily glancing down at his boots. "Walk out of the Tardis first. Before me."

She laughed, "And who decided that, then?"
"It's a commonly known but unspoken rule, Clara," he replied, arms gesticulating and eyes widening.

"Does it really matter who leaves the Tardis first," Clara pointed out, folding her arms and awaiting a suitable answer.

"Yes – who knows what could be waiting outside the door? At the very least, I can be the first to observe it. Then if it's of any danger: I'll sort it out." He clicked his fingers. "Like that."
Clara laughed again. "What are you gonna do? Wave your sonic at them? Show off your bow tie? Offer them a biscuit?" She smirked at his sudden expression of denial and mock hurt, his eyebrows close to leaping off from his face. "Let's face it Doctor, it would probably be better for both of us if I stepped out first."
He ran a hand quickly through his hair, panicking for a reasonable retort. "Ah – but I'll know where we are, the moment I step through the doors. One glance; all I need. Then I can inform you all about it as you make your way from the Tardis." He grinned smugly at her.

"Do you mean make yourself look clever," she threw back, quickly wiping away his grin. Clara swept her eyes around the room, falling back to him to say, "Go on then. Where are we?"
The Doctor faltered, eyes darting around the room. The corner of his mouth twitched; he licked his lips nervously as his fingers curled into his palms. "A room," he decided finally.

"A room."
"Definitely," he confirmed, giving a sharp nod.

Clara sighed, shaking her head.

"Wide room," the Doctor continued. "Stone floor. Stone walls. Stone columns to hold the… stone, ceiling. Someone is clearly a fan. No – no, no, no, wait," he exclaimed, raising his hands up, "Stones. Columns." He spun on his heel to find, "Big, glass, arched windows. I love a big, glass, arched window, me. And," he pointed over to, "a classic wooden door. Basic lock and key mechanism. I see." The Doctor's eyes lit up. "Castle." He grinned. "Big, grand castle. Castles are brilliant – I visit castles all the time. I say all the time, what I really mean is most of the time. Or, perhaps, just a little bit under most. Some: some of the time, I try to visit castles. No: maybe, the every-so-often rare opportunity."
"Okay, you like castles," Clara gathered with a roll of her eyes. "Which one exactly are we in? Where are we approximately? Or, when are we: that would be good to, know, too…" Her sentence trailed away. Her attention was drawn to something just beyond her, previously out of view from a well-placed column. Clara - curiosity being something she fell under without a moment's hesitation - edged closer to one side of the room, the voice of the Doctor's incessant babbling blurring to a mere dull noise as the worn object in her sight seemed to become more refined and detailed the closer she got to it.

The mirror was propped up against the dusty wall, the gold frame dulled a rotten brown along the grooves, and the reflective face cracked in multiple places. Along the top of the frame, words had been etched into. Clara tilted her head as she read the sentence, curiosity building.

"Erised…?" she muttered; albeit her voice barely a whisper, her words bounced easily around the room. The Doctor froze, her voice throwing him back to reality. He spun around to find where she had got to: moments later, Clara felt a presence by her side and she knew it was him.

"Erised," the Doctor repeated, eyes analysing the object before them. His sonic immediately appeared within his grasp, light shining as he waved it across the mirror. He flicked his wrist, the sound harsh against the sudden enveloping quiet, to examine the readings upon his device.

"What is it," Clara whispered, almost afraid to break the silence between them.

"A mirror," he replied, a laugh brushing his lips.

She sighed at him. "I know that. But a big room like this: arched windows, stone columns, door that can be and is most likely to be locked. This is the only object in the room. Most be of some importance, surely."
The Doctor ran his fingers delicately across the phrase carved into the top of the frame: Erisedstra ehru oyt ube cafru oyt on wohsi. "Interesting…" he muttered.

"Why doesn't it translate? The Tardis is here," Clara asked.

"Unless…" the Doctor's brow furrowed.

"…It's not in another language," Clara finished.

He nodded slowly, biting his lip. "Thing is," he murmured, "If it's not a different language… then what is it? Some sort of code, a puzzle maybe? But why have it on a mirror?"

His last word emblazoned through her mind. Mirror. That seemed to be of importance.

"It's not a reflection of the words, because the letters are written the right way around."

Clara frowned at him. "What?"

The Doctor glanced, surprised to hear her questioning. "Have you ever written something backwards on a piece of paper, and shown it into a mirror? Without the reflective surface, the writing will never make sense. Just looks all backwards."
"…Backwards…" Clara repeated softly. She reread the phrase with new eyes. "Maybe that's it."
"Maybe what's it?"

"The words. Maybe they're written, not reflected but simply… backwards." They shared an enlightened glance, before both simultaneously swung their heads back to the mirror.

"Ishow no tyo urfac ebu tyo urhe arts desire," the Doctor spoke, corners of his mouth curving into a grin. "Nice idea Clara, but it doesn't seem to…" he trailed off, eyebrows lifting.

Clara had the same thought. "Desire," she breathed.

They took a pause to let their gaze wander once more over the mirror.

"A mirror of Desire," Clara pondered. "What's that supposed to mean? Why is it called that?"
The Doctor frowned again at the phrase. Ishow no tyo urfac ebu tyo urhe arts desire. It couldn't have been placed there without a purpose. After all, Clara's theory had conjured the word 'desire' – the arrangement of the whole phrase couldn't have been done merely for that singular word. They all had to apply to the same rules. The Doctor paused. The arrangement of the phrase; maybe that was the problem.

He mentally strung the flipped sentence to one: Ishownotyourfacebutyourheartsdesire. His eyes widened, as Clara's studied the mirror itself.

"It's just a mirror," she sighed in final disappointment.

"Clara… think. The Mirror of Desire. What is the purpose of a mirror?"
Her nose wrinkled in thought, hair falling over her face. She brushed it away to reply, "To show a reflection of something."
"Exactly: an image. An image…" his eyes glanced to the phrase upon the mirror's frame before falling back to Clara, "Showing your possible desires."

He watched as Clara rose a quizzical eyebrow, but said nothing as she looked back into the mirror before them.

The placement of spaces between the words. That had been the puzzle to solve. The Doctor ran his eyes along the phrase again, now able to understand it for what it really meant.

He too now looked with great curiosity upon the reflective surface in front of the two of them.

Clara, not well practised in the art of patience, huffed with a pout of her lips as she found nothing new. "It's just a reflection. You and I, looking at a mirror."

The Doctor frowned. The puzzle couldn't have been put there for no reason. He observed the mirror carefully, taking in every detail. As Clara had said, their reflections were simply that: reflections. The images of himself and Clara, holding hands as they studied themselves and the mirror. She had nice hands. They were small and delicate, always decorated with simple but ornamental rings. As from what he could see in the mirror, her left hand had at least one ring, that of gold: her other hand's reflection was covered by his own. The Doctor glanced down with a smile to his actual left hand – just neighbouring Clara's right.

The Doctor hesitated. He turned back to the mirror, where the two were tightly holding hands, fingers interweaved – and back to their own hands, inches away from each other.

His mouth parted, unspoken realisation dawning. He grinned at the two beaming reflections opposite him – to find that his actual Clara had wandered back to the Tardis. He gave a final analysed glance towards the two reflections, eyes reading the phrase one last time before he retreated back to Clara's side.

"Can we go somewhere else now?" Clara asked, eyes looking up at him.

The Doctor smiled. "Yes, Clara. Anywhere you like."

She observed the honest gleam in his eyes. "What's got into you, then," she grinned, nudging his upper arm with her elbow.

"Sometimes it's good to step back and reflect on things," he mused. "Gives you the opportunity to really…" he grinned as he finished, "Turn things around."

Clara laughed fondly at him. "Are you ready to leave, Doctor?"
"Whenever you are, Clara. Lead the way." He gestured to the Tardis door.

She rose an eyebrow. "Oh really? Are you, quite sure," she teased.

"By all means," he invited, looking over her shoulder as she reached over with her left hand to pull at the Tardis door handle. He stopped her opening the door, however, when he took her hand within his own, tugging it from the handle to inspect carefully.

"Doctor - what are you, doing…?"

"You had a ring, on the finger of your left hand," he explained.

She released a nervous laugh. "No, I didn't," she replied slowly.

"But you did; I saw it in…" The Doctor paused, dropping her hand to dash back to the mirror. He surveyed the floor, "Maybe you dropped it around here somewhere."
"I can assure you Doctor that I wasn't, and haven't, been wearing any rings on my left hand today."

He couldn't help but find his eyes were drawn back to the mirror, and the two people still stood within it. He stepped over, looking at the reflection version of Clara.

There, on a finger of her left hand hanging free by her side, (whilst the other was wrapped in the fingers of his own reflection). There was a thin gold band, peppered with engraved… Gallifreyan symbols. The Doctor smiled. His reflective self must have given it to her as a gift.

"Doctor," Clara called. "Is this really that important?"

He inspected the ring another time – and stopped. For something, rather obvious, had suddenly hit him. That ring had been particularly placed. It rested upon a particular finger… for a very, particular reason. It became clear that this hadn't been just some gift.

The Doctor felt lightheaded, only to realise he'd forgotten to exhale. Doing so quickly, he re-observed what he thought he'd seen. Yes, just as he'd thought: the ring sat snugly upon that finger. And if it had been a gift from his reflective self…

The Doctor narrowed his eyes to inspect the fingers tightly wrapped around Clara's other hand. A gold ring, identical to its twin, appeared on the same finger of his own left hand.

"A Mirror of Desire, eh," he muttered to himself, adjusting the bow tie at his collar. "Well, that element certainly rings true." He laughed to himself.

The Doctor returned to his Clara, who gave him a suspicious frown. "What," he beamed at her.

"Will you ever make sense," she queried, tilting her head at him.

"Make sense?" He snorted. "Nah. Although, I can do one thing. Make promises. Not all the time, but when an opportunity arises in which a promise is required, I will go across the pathways of the universe to keep such a promise safe." He nodded to her, "I made a promise to you, Clara. My Clara. I promised to show you the stars: so," he said, offering his hand to her, which she gladly took. "Let me show you what you want to see. Let me give you what you desire most from the universe and let me seal the promise. For you."

Clara looked up at him, eyes trying to discern what lay behind those gleaming green eyes of his. Much as she adored his face, she'd be inclined if, for once, if he could show not his face. If instead, he could show her his wants, his desires. "What about you? Do you have any desires that you want to achieve to having?"
The Doctor glanced down at their hands, their fingers having automatically interlaced. A smile spread over his angular face. "At this moment, this exact moment… I have everything I could ever desire from both of my hearts."

I show not your face but your heart's desire.