Disclaimer: How I wish I owned them! Anyway, I don't; they're the property of the BBC.

Chapeau!

"I never get tired of this bit," said Donna, her hand on the catch of the door.

The Doctor shrugged into his coat. "Well, go on, then. We haven't got all day - well, we have, technically, but "

"Oh, stop your babbling!" Donna said, opening the door. "One day the bleeding world'll end while you babble."

"You're one to talk!" exclaimed the Doctor, following her outside. "And I'll have you know that I've actually saved the world several times merely through the power of words. So did Shakespeare. Genius, that man." He looked around. "So, where are we?"

The TARDIS was parked in the middle of a busy street, the people flowing around it as though it was not there. At first glance the Doctor thought he must have brought them to Earth by mistake, but they didn't feel human, and there was something something not right, but he couldn't put his finger on it.

Donna turned round and went back into the TARDIS, and he followed her. "What is it now?"

"Hats," she said.

"Hats."

"Didn't you notice?" she demanded.

"Notice what?" asked the Doctor.

"They're all wearing hats!" said Donna, heading off towards her bedroom. "Every single person, or alien, or whatever that lot are - they're all wearing hats."

The Doctor went and had another look. She was right. The people passing by on the street were all wearing hats - all manner of hats, from those that resembled trilbies and bowlers and flat caps, to bejewelled scarves and elaborate contraptions that were definitely not of human make.

He found Donna in front of the mirror in her room, trying on hats from her hatbox. "Didn't I tell you," she said, posing with a floppy sunhat, "that if we came to the Planet of the Hats, I'd be ready?" She swapped the sunhat for a rakish boater.

Rubbing his eye, the Doctor conceded she had a point.

"So why are they all in hats, anyway?" asked Donna, replacing the boater with a woolly hat with a bobble, before going back to the sunhat.

"I really don't know," the Doctor said. "Are you done?"

"What about you?" Donna said, closing the hatbox. "You've got to have a hat too."

The Doctor drew himself up to his full height. "I am past hats," he said, remembering a succession of hats during earlier regenerations and shuddering. "Anyway, hats with this hair? I like my hair. I refuse to cover it with a hat. Just because they're wearing hats doesn't mean we have to wear hats."

Donna raised an eyebrow at him. "Yeah? Maybe it's a law, or something."

He offered her his elbow. "Laws are there to be broken," he said, hoping he sounded reasonably impressive. "C'mon."

Back outside it had to be said that every single inhabitant was indeed suitably coiffed, and within a few metres of the TARDIS the Doctor was feeling the glances of a hundred behatted citizens on his own bare head. He squared his shoulders and carried on walking, Donna's arm tucked in his, trying to blend in. He was good at blending in, dammit!

"So, where are we, anyway?" Donna asked, admiring a flowered concoction on the head of a woman carrying a baby (the baby wearing a bonnet).

"Planet of the Hats," the Doctor said. "I don't know! Part of the fun, not knowing." He looked around, at the bright sun and the colours of the buildings and the scent of beeswax in the air.

"Thought you knew everything," she said with a grin.

"Well," he said, "bipedal humanoid shape, and the air's your standard mix, but I don't think they're human. Too uniform, for starters. You lot, you're all about your individuality."

"They have different hats," Donna pointed out.

The Doctor shook his head. "But they're all wearing them." He gestured at a man ahead in a truly impressive top hat. "Look at his, though. That's a hat. That's really a very good hat."

The man produced a kind of bulbous truncheon from somewhere about his person, and held it up in what was definitely a threatening kind of a way. The Doctor unhooked Donna's arm from his and took her hand.

"Donna?"

"Yeah?"

"Erm fancy a run?"

They ran. But either the man with the truncheon had a double, or he knew a shortcut, because he appeared in front of them as they skidded around a corner. The Doctor, mentally, voted for the shortcut, and put up his hands. "All right, you've got us. What've we done?"

"Abomination!" said the top-hatted one. "How dare you show your " he waved his truncheon in the direction of the Doctor's head.

The Doctor stared for a moment. "Oh, my hair!" he said. "It's perfectly normal, you know."

Donna elbowed him.

"I knew it was against the law, not to wear a hat," she said. He looked at her, and she shrugged. "You can thank me later, when you've got us out of this."

The man with the truncheon beckoned a friend, in a matching top hat, and they marched the Doctor and Donna through the streets, into a building, and into a cell. The door clanged shut, and the Doctor felt the stinging of a slap across his cheek.

"Eh! What was that for?" he demanded.

Donna sat down on the wooden bench in the corner. "For getting me imprisoned. Again. We're always getting bloody captured."

"Not always," the Doctor said, taking his sonic screwdriver out, slipping on his glasses, and beginning to examine the door. "Often. Not always."

She made a sound that could have been a harrumph, and fell to silently watching him as he buzzed the screwdriver at the lock. It was a good lock, too; better than the screwdriver, for once. He gave up, and joined Donna on the bench.

"Sorry," he said.

"You're always saying that," she returned. "Always sorry for everything."

He looked at her, knowing she was right. "Well, I am sorry, for everything. I've got a lot to be sorry for."

"Well, stop being sorry now and get us out of here!" Donna exclaimed.

The Doctor waved the screwdriver at her. "It's not working."

"So what's the plan?" she asked.

Looking around the bare cell, he shrugged. "Talk our way out. It usually works. I will get us out of here, Donna, I promise; preferably without a hair on our heads being harmed." She adjusted her hat. "And don't say anything about me and hats," he added quickly. "Where d'you want to go next, anyway? Somewhere warm? Somewhere cold?"

"We've just done cold," Donna pointed out. "How about somewhere relaxing?" The suggestion was barely worth dignifying with a response, so he gave her a look complete with raised eyebrows. "C'mon, you must know somewhere relaxing?"

"I don't do relaxing," he said.

"Maybe you should," she suggested. "Might be good for you."

"Weeelll," the Doctor said, "there is this little planet out beyond the Monastic System. Has a nice spa. Famous for its hot springs - it's all to do with the substance of the planet, high sulphur content, and the way the rock's formed. Fascinating place. I haven't been there for, oooh, centuries. Took a friend of mine there once." His mind flicked back to the trip with Sarah Jane - not that long before the call from Gallifrey had come - his scarf had got slightly frazzled by the steam. "Anyway," he said, wrenching his thoughts back to the present, "it's an option."

"Sounds great," Donna agreed. "But what about "

She did not finish the sentence as the door opened, and two of the top-hats hauled them out and along endless corridors to what was indubitably a courtroom. The Doctor glanced at Donna; she gave him a severe look in return and mouthed, "Get us out!"

In the judge's seat there was an extra-tall top hat - for a moment the Doctor thought there was nothing but a top hat, but then he realised there was a very small man underneath it. The judge motioned the Doctor and Donna into wooden docks.

"Strangers, you are found guilty of appearing in the public gaze bareheaded," the judge intoned. "By the most weighty laws of the Chaporin Nation "

"Oh, you're Chaporins!" said the Doctor, several details clicking at once - the hats, the particularity of the light spectrum, and the dull similarity of the people.

"The prisoner will not interrupt the court!" said the judge.

"The prisoner just did," the Doctor said. "Look, y'r Honour, it's an honest mistake. And really it's only me that hasn't got a hat on, because my friend here does. Look. It's got a good big brim and everything."

The judge harrumphed, thoughtfully.

"And anyway," pursued the Doctor, warming to his theme, "I don't need a hat, not like you. It's the suns, isn't it? Without something to cover your heads, you'd all come out in very unsightly boils - and I really do think you've got a good solution, it's brilliant, really, although you might think about letting people match their clothes to their hats occasionally." Donna was staring at him as if he had gone mad, but he ploughed on. "And vitamins. Increase your vitamin intake - more vegetables - and you might find you'd be able to take your hats off, occasionally, on a cloudy day."

"Who do you think you are, prisoner?" the judge said, standing up, his face florid and furious.

"I'm the Doctor," said the Doctor, grinning, "and you're going to let me and my friend leave. I promise if I come back I'll put a hat on. Honest." He turned to Donna. "C'mon."

He climbed over the low wooden wall of the dock and held out his hand to Donna. Copying him, she took it, and they walked out.

"Just keep walking," he murmured to her. "Nice and confident. Straight ahead. I think I've talked enough to stop them following us for a few minutes. Bamboozled, that's what they are, bamboozled. The Chaporins are notoriously simple, that's why they went for hats with their sun problem." He pushed open the door of the court building and they stepped out into the bright sunshine. "They're ridiculously sensitive to ultraviolet light, and they have two suns, which only compounds the problem, so they went for hats."

"That's great," said Donna. "Really, great, but there are people following us "

They ran, again, Donna holding on to her sunhat with one hand and clutching the Doctor's hand with the other. This time their pursuers did not employ any short cuts, and they made it back to the TARDIS breathless but alive and well and with all hairs, and hats, intact.

He put the ship into the Vortex and was savouring the feeling of a successful escape when Donna took his hand and towed him, protesting, to the wardrobe room.

"Right then," she said, sitting down in the sofa that had somehow appeared in the wardrobe, "hats."

"Hats."

"I'm not being arrested again because someone's lacking a bit of headgear, mate," Donna said. "Show me your hats, mister."

A cupboard door swung open, and several regenerations' worth of hats fell on to the floor. The Doctor sighed; this was evidently one of those occasions when the TARDIS and his companion were ganging up on him. Bending over, he picked up the dusty deerstalker hat that had seen him past Magnus Greel all those years ago. He put it on; somehow squashing floppy hair was harder than squashing curls. Donna laughed.

"Eh!" he said. "I'll have you know this was a good hat."

"When did you last wear it?" Donna asked, curling her legs up underneath her on the sofa.

"Well," he began, "it was a dark and foggy night "