“When I said I wasn't mating with you, I actually meant it.”

The Doctor looked up from reading an old (or, in the TARDIS, possibly as-yet-unprinted) copy of Heat magazine. “Okay,” he said, confused.

“I don't want any of your funny-business,” she continued.

“My... my what?”

She put her hands on her hips. “I know what you're like. 'Ooh, Martha totally fancied me. Ooh, I got off with some famous aristocrat.'” She waved her hands about as she imitated him, badly.

The Doctor blinked at her. “Why are you telling me this?”

“Where are my knickers?”

The Doctor turned a bit red around the ears. “I expect you're wearing them.”

“Of course I'm wearing knickers! Oh my God, did your other women just wander around half naked all the time?”

“No!” he protested, blushing harder now. “Not that I'm an expert on my friends' underwear, but as far as I know they... wore some.” He scratched his chin. “Possibly Jack didn't, but he's a law unto himself. And there was Jamie, but that was a cultural thing and I didn't want to-”

“My knickers,” said Donna, “are missing. I put them in that thing you call a washing-machine, and now they're gone.”

The Doctor shrugged, somewhat relieved. “Did you check inside the machine?”

“Of course I did.” She glared at him. “Give them back. Now.”

“Donna, I haven't stolen your underwear!”

“Oh? Who else would it be? There's only you and me on the TARDIS.”

“Look,” said the Doctor, in what he felt was a reasonable tone, “if I really wanted some women's underwear I'd just buy some in a shop. I wouldn't have to steal yours.”

“And I know you must use the laundry a lot, because you've only got two suits,” she said, somewhat triumphantly.

The Doctor stood up and took off his reading glasses. “Right, I'll prove to you that I haven't stolen anything. They've probably just slipped inside the mechanism.”

Donna followed him to the laundry room. When they arrived he bent down to look into the machine only to be stopped by Donna prodding his shoulder.

“Oi,” she said.

“What?” he asked, wearily.

“If you do find anything, you've not to look at them.”

The Doctor frowned up at her. “How am I supposed to find them if I'm not looking?”

“Use your other senses.”

“Yes,” said the Doctor, “I'll use the famous Time Lord knicker-sonar instead of my eyes.”

Donna narrowed her eyes. “Don't get sarky with me, you skinny alien pervert.”

The Doctor looked into the washing-machine. “You know, Donna, that your nearest living relatives use sexual play as a form of social glue. So if either of us was to fit the title of pervert, I'm fairly sure it would you.”

Okay, maybe that hadn't been the most thought-out response to her accusations. “Excuse me?”

Pan paniscus, the humble yet extremely friendly bonobo. Ninety-eight percent identical in DNA to humans.”

“Are you calling my species a slag?”

The Doctor held up a hand in case she decided to hit him or throw something at him. “I would never do that, I'm merely pointing out that compared to Time Lords you lot are a bit... randy.” Yes, that was the right word.

“Hah!” said Donna. “I haven't even had sex since before I met you. Whereas you -”

“What about me?”

“That blue woman with all those tentacles?”

“She was showing me her etchings!” he protested.

“What, all night? No wonder you looked so shag-dazed in the morning.”

The Doctor sniffed. “A Time Lord never tells, but I did not have sex with that woman.” He turned his attention back to the matter at hand. “What did they look like?”

“What did what look like?”

“Your...” he waved a hand at her, “undergarments.”

Donna drew in a scandalised breath. “They look like knickers! And no they're not all lacy and crotchless, don't get your hopes up.”

He peered into the washing-machine. “Well, I don't see anything.” He ran a hand around the drum. “I'll have to open it up,” he said. He pulled the sonic screwdriver from a pocket and unfastened the panel on the top.

Donna glanced inside. “It's a bit gooey,” she said, a hint of disgust in her voice.

“She's bio-mechanical,” said the Doctor, defending his TARDIS.

“Fine, but if my knickers are in that, I don't think I want them back.”

The Doctor shoved a hand into the slimy depths of the washing-machine. “I don't think there's anything in here.” He felt around inside it. “Come on, Old Girl, what have you done with them?”

“So now you're saying that your spaceship stole my underwear?”

“I'm not saying that. Why would she need to steal them anyway?” He pulled his hand out and wiped it off on a nearby towel.

“Has anyone else ever complained about lost laundry?”

“You're the first, apart from occasional socks going missing.” He scratched the back of his neck. “I like to add an extra, unwanted, sock to any load of laundry. As a sort of sacrifice to any vengeful sock gods.”

“Is that a Time Lord thing?” she asked.

“Yes, Donna,” he said faux-solemnly, “those were our gods. Time, Death, Pain, and Sock-Thief.”

“Winding me up isn't going to help find my clothes.”

He raised his hands in a gesture of surrender. “I'll buy you some more.”

“I don't want new ones, I want the ones your time-machine ate!”

“She doesn't eat pants.”

“Well, it's not like she runs on the mains, is it? She has to get fuel from somewhere.” Donna had a theory and she was sticking to it.

“Maybe was a wormhole,” the Doctor speculated. “Just a small, unstable one, and that's where they went. To the other side of the universe. We'll never find them. That could explain some of the socks as well.

“That's a bit unlikely,” said Donna.

“It's a lot more likely than the TARDIS eating them or me nicking off with them,” he complained.

“I liked the ones with the little strawberries on,” she said, wistfully. “Those were some great pants.”

“I'm sorry for your loss.”

“No you bloody aren't,” she said. “And now you're imagining me in nothing but strawberry-covered knickers, aren't you?”

He hadn't before she'd said it, but he could tell that wasn't what she wanted to hear. “I'm not, and the thought of you naked has never crossed my mind,” he lied. He was ever so good at lying.

“Oh, please,” said Donna. “You might be an alien, but you're still a man.”

“I'm a Time Lord,” he said, “we're above that sort of thing.” A thought occurred to him. “Have you been thinking about me naked?”

“I beg your pardon?” shrieked Donna.

He shrugged. “I don't mind if you have, I know you don't mean it sexually. It's just like erotic dreams, it's automatic, it doesn't mean you want to sleep with someone.”

Donna looked at him through narrowed eyes. “Doctor,” she said steadily, “if you're admitting to having sex-dreams about me then so help me God I'm going to castrate you in the night.”

“I didn't say that!” he cried, with a healthy sense of self-preservation. He resisted the urge to cup a protective hand over his groin.

“It sounded a lot like it to me,” said Donna, dangerously.

“Yes,” he said, “but as we've established you're a chromosome away from shagging everyone you meet as a form of polite greeting.” His mouth fell open as he realised what he'd just said.

“Oh, you're looking for a slap,” she told him.

“I'm sorry, it just came out.”

“You need to think before you open your mouth, Spaceman.” She pulled herself up to her full, still not that impressive, height. “How many times have do I have to tell you that I'm not interested in you?”

“Maybe if you didn't protest so much it would be more convincing,” he said, recklessly.

It really, really hurt when she slapped him. The Doctor staggered backwards against the washing-machine and rubbed his cheek with a hand. She was a lot stronger than she looked. It was one of the things he liked about her.

“Right,” she said, “I'm going to my room. You can call me when we're at a Marks & Spencers, and you'd better have your credit card ready.” She walked out the room with her head held high.

The Doctor looked at the washing-machine that had betrayed him. “And don't think I'll be cleaning out your gyroscopic regulators any time soon, Old Girl,” he said bitterly.