Set during the New Earth episode, my favourite. My little sister refers to it as the 'body-switch' episode, even if it is just possession. Anyway, I decided to write my own version to fit my sister's theory, seeing as though I love body-switch stories.

I've used a lot of the original material from the episode, please don't hate me.

"We're trapped!" Cassandra cried with Rose's voice. "What are we going to do?!"

The Doctor looked unusually stern.

"Well, for starters, you're going to get out of that body. That psyhcograph is banned on every civilised planet." He looked even angrier as he circled her. "You're compressing Rose to death!"

"But I've got nowhere to go," Cassandra muttered. She turned and glared at the Doctor. "My original skin's dead."

"Not my problem," the Doctor retorted. "You can float as atoms in the air. Now, get out."

Cassandra gave a smug smile.

The Doctor held out his sonic screwdriver and pointed it at her. "Give her back to me."

"You asked for it," Cassandra said quietly, and Rose's voice sounded dangerous. She began to breath in deeply.

The Doctor looked puzzled for a second. And then, suddenly, he realised what she was about to do.

A brillant red light shot out of Rose's body, heading straight for the Doctor. He felt it enter him, and then, just as quickly, he felt his own mind drawing together painfully. He closed his eyes.

Both Rose's body and the Doctor's stumbled, coughing. The Doctor glanced up. "Ow, that hurt..." he muttered. Then he suddenly realised what he'd said. Or rather, how he'd said it.

He glanced down at his hands. They weren't his. They were someone elses...

"Well, this is... odd." He heard a voice say. A voice he knew very well.

"Very good, Cassandra," the Doctor groaned, standing upright. "I don't know why I couldn't see you were going to go into me."

The Doctor was staring at himself. Or, more correctly, Cassandra in his body.

"Go into you?" Cassandra replied, surprised. It was the Doctor's voice, but there was a slight tone, a raised edge that hadn't been there before. "No, I went into the..."

She stopped talking abruptly, looking confused. "I may be the Doctor now, but I still hear Rose in my mind," she mused.

"That's because no one told you," the Doctor explained, still examining the body he was in. "Us Timelords, we don't like having people possesing us. If anyone tries, we kind of... take on the body of the closest living thing in the room? The soul in the closest living thing, see, then goes out into someone else."

Cassandra screwed up the Doctor's face in concentration. "So... You're the Doctor?"

The Doctor glanced at his hands again. "In mind, yes. In body, no."

Cassandra began to laugh. "Oh, this is rich. The Doctor, now the assisstant." She flashed the Doctor's grin. "And the assisstant, now inside the Doctor."

The Doctor didn't say anything. Cassandra grinned again.

"And your body... well, it feels different from what I'm used to." Cassandra ran her hand down her side. "Goodness me, I'm a man!"

The Doctor rolled his eyes. God, this was turning into a weird day.The last human on Earth was in his body, and he was in Rose's. Just great.

There was a loud crash, and Cassandra jumped about six feet in the air. Both of them turned to see the diseased people louping towards them, having broken through the door.

"What now?!" Cassandra cried, backing behind the Doctor. "What do we do?! What the hell do we do?!"

The Doctor swivelled around. "Up the ladder!"

Cassandra pushed in front of him. "Out of the way, blondie."

"Blondie?" the Doctor repeated, clammering up after her and shaking Rose's hair out of his eyes. "That the best you can come up with?"

They both climbed as fast as they could. The Doctor had to keep pushing his hair back. Is this what it's like for Rose? he wondered. Why didn't she just cut it short?

"Please...help us.." the diseased corpses were calling, gathering around the base of the ladder. Slowly, they began to climb after them.

"You had to go into my body, didn't you?" the Doctor called after Cassandra. "We might have stood a stronger chance if I was myself!"

Something grabbed his ankle and he instinctively looked down.

"All our good work," Matron Casp was saying, keeping a tight hold on the Doctor's foot. "All our healing! The good name of the sisterhood! You've destroyed everything!"

This time, Cassandra rolled her eyes. "Go play with a ball of string," she advised the matron sarcasticly.

"Everywhere! Disease!" Matron Casp hissed. Her words suddenly changed into a yowl as one the disease carriers reached out and touched her bare skin. Her feline face grew boils and she suddenly let go of the ladder, falling down and hitting the bottom with a sickening crunch.

"Move! Move!" The Doctor ordered in Rose's voice, herding Cassandra up the ladder as the bodies drew closer.

Cassandra reached the top of the ladder first and began banging on the closed door. "It's locked!" she cried. "Now what do we do?"

"The Sonic Screwdriver," the Doctor said quickly. "It's in my inside pocket."

Cassandra pulled it out, glaring at it dissapprovingly. "You mean this thing?"

"Yes!"

"Well, I don't know how, do I? You're the Doctor, not me!"

The Doctor mentaly smacked his forehead. "Go into one of the disease carriers so me or Rose can do it!"

"No!"

"Cassandra, do you want us to survive or not?!"

Cassandra glared angrily at him, then drew a deep breath. "I am so going to regret this," she muttered. The brillant red light came out of the Doctor's body and passed the real Doctor. It absorbed itself into the closest of the diseased bodies, which stopped dead as Cassandra took possession.

The Doctor turned back to where his body stood, looking confused. "Rose," he said quickly. "Use the sonic screwdriver to open the door."

"But I'm you..." she started to say in his voice.

"Just do it!" the Doctor shouted. Rose looked scared for a moment, then took the screwdriver and switched it on, holding it up to the door. After a few seconds, the door clicked open and Rose began to scramble into it, moving oddly in the Doctor's body. The real Doctor clambered in after her and grabbed the screwdriver, holding it to the door.

Just before the door slammed shut, the red light zoomed in and went into the Doctor. The Doctor felt the aching pain again and closed his eyes. When he opened them, he immediatly glanced down at himself.

"Yes!" he exclaimed. "It feels so good to be me again, now I've gotten used to this body."

Rose's body sat on the floor, breathing fast. She looked up as the Doctor spoke.

"So you're you again," she muttered, folding her arms.

"Yes, and you're still Cassandra in Rose," the Doctor replied. "We've really got to change that."

Cassandra glanced at him and he held his arms up in surrender.

"Just no more body-switching again, okay?"