'Now, this part, Martha... This part is very interesting.'

The Doctor pointed to a diagram in a huge, ancient book and continued. 'See. All these extra bits and bobs... How do they all fit in?'

Martha peered at the book. She had no idea.

'Most organs are smaller. I have two hearts, but they are smaller. And more efficient. Naturally. I'm really a bit of a medical marvel, even if I am getting on a bit. Fit as a fiddle, me.' He grinned widely at her. 'Anyway, the organs are smaller but work at a higher level - huge lung capacity but I have a respiratory bypass system - can go without air for a while. Not for long, but it's certainly handy...'

He went to turn the page, but Martha stopped him.

'Is everything smaller?'

'Well, as I said, most are.'

'Just internal organs? What about external?'

The Doctor looked at her in something akin to shocked surprise. 'Martha Jones, I am surprised at you!' he blustered 'I... I...' He shook his head. 'I am lost for words, really. And not very often that happens, to be honest, as you well know.'

'I'm just interested. Medical curiosity. What if something happens to you, how do I know if you look 'normal' or not?' Martha said as seriously as she could. She wasn't being very successful.

'I am perfectly normal, I'll have you know. I'm glad you find it so funny.' He slammed the book shut. Martha began to protest and say she was sorry when he stopped her.

'As you are so interested, let's have a look at a live specimen, shall we?' He looked around, as if searching for something, stopped and then ambled up to Martha, hands in pockets. 'Oh. That would be me, then.' He unbuttoned his jacket and shirt, shrugging them off and then pulling at his tee shirt, all still within centimetres of Martha.

'Doctor, what are you doing?' She backed away slightly, until she hit the end of one of the tables in the TARDIS library.

The Doctor was now unzipping his trousers as he moved forward again, this time pressing himself against her as he stepped from his clothes, completely naked.

'Enough studying of books, Dr Jones... Time for a practical... Examination.' He slid a hand around her waist and pulled her to him, kissing her soundly. 'It's exam time. Let's see if you and I pass...'

He soon had her as naked as he was and sitting on the library table as he kissed down her body, making, he said, 'a through examination of her for his records.' The fact that his examination included liberal use of his tongue in various areas did not upset Martha one bit and she gave him a 'A-', only deducting points for not paying equal attention to her left breast as he had to her right.

He now stood between her open thighs as she kissed down his chest, charting the muscles of his back with her fingers. She was orally examining his nipples when she reached down to stroke him and stopped as she took him in her hand.

'Ahh.'

'Martha?'

She bit her lip, trying not to laugh. So it was external organs as well. Oh, dear. What was she going to say to him? 'Nothing...'

'What is it about that tone of voice and that face that makes me not believe you?' He kissed her forehead.

'No really. Nothing. It really is...' She stroked him 'Nothing.' Oh, God. This was not going well, she thought.

'Good.' He smiled at her, a smug smile that seemed quite out of place in the circumstances. 'Because, my dear and lovely doctor Jones, I have a surprise for you.'

He suddenly pulled her to the edge of the table, pushing her thighs open wider and guided himself into her, thrusting hard.

Martha's eyes widened and she gasped. He was filling her completely, feeling huge and hard inside her, hitting just the right spot that made her shiver. He withdrew from her all the way and thrust again, making Martha groan with pleasure and he filled her again. She grasped his shoulders and looked at him. The Doctor grinned at her one of his hugest, most self-satisfied grins.

'So, Martha Jones, what have we learned today?' He thrust back into her. 'That Time Lords have some smaller, but superior functioning, organs.' Thrust. 'And of course, being a Time Lord I have one constant advantage.' He thrust once more and bent to nibble Martha's earlobe.

'What's that?' Martha squeaked breathlessly.

He moved his lips from her earlobe to whisper low to her.

'It's bigger on the inside.'