After they'd got back to the TARDIS, she'd quietly excused herself "I'm fine," she insisted with a weak smile. "Really." The Doctor didn't really think much of it; it had been a tiring day - even more exhausting for a human who'd never been outside their home planet before. He smiled softly to himself, remembering an eager young boy feeling very similar after his first adventure. How long ago that seemed - how far he'd come, how far he'd fallen. He couldn't make the same mistakes again – not with Clara. The emotions he felt around that girl almost scared him – almost.

This Doctor had never really been one for romantics, preferring to see the universe, to explore as much as possible. Any attempts at a kiss usually resulted in him flailing his arms around like a fish out of water until the incident was finished with. Not that he was opposed to physical contact - hugging was fine. Hugging was good! He couldn't deny a good hug. Even a kiss to the hand or the forehead was nice. But involve any mouth to mouth action and he was instantly out of his depth. Not that the Doctor could ever be intimidated by such a silly human habit. Of course not.

But, unsurprisingly, everything about this girl was different. She'd truly captured his hearts – daft human expression, he thought. It wouldn't be possible to have your heart captured and still be alive – less of a loving gesture, more like brutal murder. He briefly wondered whether the saying was derived from some old (and sick) human ritual. Nevertheless, figuratively, if the heart was the thing that dealt with emotions and, metaphorically, a person could capture it, she'd well and truly got his –both of them - under lock and key.

Feeling an overwhelming urge just to be with her, to assure himself she really was alright, he left the control room, trusting his feet to lead him where he needed to go. He finally found her in the library, hunched up on the sofa with her book cradled to her chest.

'Can I?' he said, gesturing to the spot beside her.

'Feel free,' she whispered, continuing to stare straight ahead.

He looked at her thoughtfully for a moment. Clara Oswin Oswald - the impossible girl, the woman twice dead. She simply did not realise how absolutely incredible she was, and that only added to the overwhelming curiosity and – yes, he had to admit it, attraction he felt towards her.

'That was a remarkable thing you did back there,' he finally said. 'Not many people would have had the strength to give up something so close to their heart. You really did save thousands of lives, Clara Oswald,'

The sound of her name stirred something inside Clara. 'I miss her,' she croaked, her eyes threatening to spill the tears that had built up there. 'I think about her every day – about what could've, what should've been,'

The Doctor's hearts broke at those last few words as his mind turned to all those he had lost, all those he had turned away. His arm somehow found its way to her shoulder and she curled up into his side.

'But,' he began softly, stroking her back comfortingly. 'By giving up what should have been with her, you saved what will be for a generation, and generations to come. You used an infinity of memories that could have been to give thousands of others a chance to make memories of their own.' He gently brushed a strand of hair away from her face and kissed her forehead.

After a few moments of silence Clara spoke up. 'It was her, really...she did it. And she'd be so happy, y'know, to have saved all those people,'

She turned her face up to look at the Doctor and he didn't really know why he did it; she looked so lost and hopeless and desperate for reassurance, so he kissed her. The very thing he'd been dismissing mere minutes ago, and he'd gone and initiated it. Of his own accord.

Their position was very uncomfortable – his arm was twisted around her back whereas her arm was trapped between their bodies. And the Doctor felt absolutely terrified. He had to admit it to himself – he had no idea what to do. Stupid, stupid humans and their silly habits.

Their lips moved frantically against each other's, searching desperately for a rhythm, when suddenly something clicked. Clara, initially shocked by the unexpected embrace, shifted her weight to the side and lifted her hand to his neck, pulling his body closer to hers. He complied by reaching his other arm around her to rest on her waist, not daring to think about the situation too much for fear he would do something terribly, terribly wrong. Instead he – what term did the humans use? Trusted his instincts. The passion began to die down and the kiss turned sweeter, more gentle. Clara's hand moved from his neck to gently caress his cheek and his thumb stroked up and down her side.

They finally broke apart, but neither felt the need to say anything. They simply grinned at each other, a sense of mutual understanding in the air. Maybe, the Doctor thought, maybe kissing wasn't such a silly human habit after all.