Disclaimer: Doctor Who belongs to the BBC. I do not own any of it, nor do I get paid for it.

A/N Thank you for the response on the last chapter. As promised, here is Part 3 with further action and explanations.

Happy Reading!

New Earth: Devil You Know

Previously

Fitz could only watch in horror when Cassie realised that there was no escape and decided to just run through the window to jump out of the flat. It was a sheer drop and Fitz knew that it was impossible to survive.

"She's gone," said the man as he ran to the window and peered out. "We won't be able to catch up with her."

It was all too much for Fitz, who promptly passed out.

Several hours ago

"We've been going around in circles," said Rose as the Doctor readjusted the tracking device again.

It was the oddest one Rose had seen yet. The Doctor had unfurled the round socket and used the delicate metal to make an old-fashioned cross. There were wires going around them, which held them in place but also connected the circuit.

"The signal keeps changing," he said, starting to sound a bit frustrated too. He was supposed to be taking Rose somewhere to relax and enjoy, not drag her around London in search of an anomalous signal. He realised that they had been searching since that afternoon and the sun had gone down a while ago. He sighed and looked at her apologetically.

"Tell me what exactly we are looking for," she said.

"A possessed person," he said.

"Possessed by what?" asked Rose, her mind immediately jumping to the Mara, before being reminded of demons. She didn't voice it though, because she was certain that demons didn't actually exist.

"That is a good question," he said. They passed by a chippy and he stopped. "Come on, let's go have some chips and get something to drink."

Rose nodded at once, grateful for the break. The chippy was more or less like the hundreds of the sort around the London that Rose remembered. So far, she hadn't seen a glaringly obvious difference to her old universe but if what the Doctor had said was right, then the Time Lords had found the universe most closely compatible to their old one.

The Doctor found them a booth while Rose ordered chips and some fizzy drinks for the two of them. A quick look at her watch told her it was past 7 and she hadn't eaten since breakfast. No wonder she was ravenous. By the time she returned to their table with their drinks and two baskets of chips balanced in her arms, the Doctor had covered the table with what looked like the entire contents of his pockets.

"Should I even ask?" asked Rose, raising her eyebrows as he hastily began to clear up space for her to set down the chips and drinks.

"I'm looking for a flask," he said, plunging his entire arm inside his coat pocket.

Rose noticed the middle-aged woman at the next booth raise her eyebrows at the seemingly impossible action. "Magician," Rose told her as a means for explanation. She turned back to the Doctor who had procured a flask from the depths of his pockets and was holding it up triumphantly. "What do you need that for?" she asked, picking up the vinegar to dunk on her chips.

"Oh, perfect," he said, snatching the bottle out of her hands and emptying it inside the flask.

"Oi! I was about to eat that," she said indignantly. "Why are you putting vinegar in that?"

"Acetic acid acts as a mild skin irritant for post psychological transplant patients," he said, starting to cram the odds and ends back into his pockets.

"Post psycho-what?" asked Rose, trying a chip without the vinegar before making a face and grabbing the bottle from the next table.

"Psychological transplant, or an easier way would be to call it 'possession'," he said, grimacing at the amount of vinegar she was pouring onto her chips. "Mind of one person, the body of another."

"There's technology that can do that?" asked Rose incredulously. "Which idiot came up with that?"

"A very odd human being named Dr. Charles Davy," said the Doctor. "He disappeared shortly after his invention, so he wasn't around to see the destruction his little transplant device caused. The so-called psychograft has since been banned on every civilised world."

"But how come it's here in 1963?" asked Rose.

"Good question," he said. "It will be at least four and a half billion years before it will be invented. That is what worries me."

The two of them ate quietly for a while as they contemplated possible scenarios that would explain such an advanced and futuristic technology being in use. "So your tracking device will be finding the transplant thingy, will it?" she asked, looking at the contraption speculatively.

"No," he said. "It will be tracking the person on whom the psychograft has been used."

Now

"He's just fainted," said the Doctor. "Culture shock, that is all."

"I saw him this morning," said Rose as she pressed a cool cloth to Fitz's head. "He works at a flower shop just down the road."

"Did he tell you his name?" asked the Doctor.

"Called himself Fitz Fortune but said it wasn't his real name," she said. Fitz stirred and groaned in pain. "You alright, mate?" she asked him.

"Jesus Christ, my head hurts," he groaned.

"That's cause you fell like a sack of potatoes and hit your head," said Rose as she helped him sit up.

"We have to go," said the Doctor urgently. "Someone's called the police. This might be a bit difficult to explain."

Fitz blinked stupidly at him and then looked between the two of them. "Who the hell are you two?" he asked.

"Oh, our apologies," said the Doctor pleasantly. "I'm the Doctor, this is Rose Tyler. Now, Fitz Kreiner, I believe it is time to run."

Fitz barely had any time to react before the Doctor and Rose hauled him to his feet and pulled him along with them. He half-stumbled, half-ran, using two of them to support himself since his legs still felt a bit wobbly and his head hurt like hell. The police were starting to gather near the building, but the Doctor and Rose pulled him towards the back alley which was quite empty.

"We can't stay here. We have to keep moving," said Rose, looking around at the crowd that was starting to gather.

"Right, I've had enough," snapped Fitz, trying to sound angry but his voice came out oddly squeaky. "What the hell was with that demon girl? And who are you two? How did you know my name?"

"All very excellent questions, but we have to keep moving," said the Doctor. "Is there somewhere we can talk?" he asked Fitz.

Fitz stared at him incredulously but nodded dumbly. "Molly's pub," he said. "This way."

Cassie slammed the door open as she stomped into the house. Charles emerged from the kitchen and stared at her in horror. "What in the world happened to you?" he asked, taking in her dishevelled and bloodied appearance.

She snarled angrily at him and grabbed his neck in a vice grip. "You said the psychograft was successful," she yelled as he started gasping for breath. "This body started falling apart in one evening!"

"Let him go, Cassie," snapped Hannah, who had run into the room having heard the screams.

"Stay out of it, you bitch," Cassie snarled at Hannah. But she loosened her grip on Charles' neck. "We worked so hard for this and you told me it had worked!"

Charles was wheezing as he tried to control his breathing. "I...thought it had," he said panting. "The girl's body must have been too weak."

Cassie took her hands off his neck and started pacing angrily. "We found the perfect girl. Blonde hair, blue eyes, just six months shy of being eighteen, even with a name similar to mine. We exposed her to a daily resonance pattern of sonic waves to make sure that the psychograft could be permanent," she said. "What are we going to do now? We need a new body."

"At such short notice? It will be hard," said Hannah. "What about the sonic resonations?"

"The sonic resonations are inconsequential after the first transfer," said Charles. "Any body will do, but we have to act fast," he added, looking at Cassie whose body was starting to develop lesions.

"Anyone would do?" asked Cassie contemplatively.

"Yes," said Charles.

"Good," she smirked before advancing towards Hannah.

"No," Hannah gasped. "You can't! Charles, stop her!"

"You've outlived your usefulness, Hannah," said Cassie. "You're old and dry, and really godawful ugly, but beggars can't be choosers. You will do very nicely until I find another one."

"NO! Please, don't!" Hannah screamed as a silvery mist escaped Cassie and shot towards her body.

Cassie's body fell to the floor and Hannah stood up straighter, with a triumphant smile. "Ah," said Cassandra/Hannah. "Not as much fun as that one was," she added, nudging Cassie's body with her toe. "Get rid of it," she snapped at Charles.

"How?" he asked, looking a bit shaken at hearing Cassandra's orders through Hannah's mouth.

She paused at his question before a slow smirk appeared on her face. "Dump her body outside the hovel they call Molly's pub on Mercer Street. The rest will take care of itself."

"...and her eyes were white. Like a succubus. I'm telling you, she was a demon!" Fitz rambled on, downing his third glass of sherry.

"Perhaps enough of that," said the Doctor, gently prying the rest of the bottle away from Fitz. He exchanged a look with Rose, before turning back to Fitz. "So, you met her here?"

"Yeah," he said, reaching into his jacket for his pack of cigarettes. "Either of you got a light?" he asked.

"No," said Rose with a grimace. "You really shouldn't smoke, you know. It gives you cancer."

"Give over, doll. As if that's really true," he said, searching his own pockets for some matches.

"Actually it is," she said, narrowing her eyes at his dismissive tone. "Tobacco is bad for your lungs…"

"Rose, perhaps not now," interrupted the Doctor. "Fitz, hold off on that cigarette which is indeed harmful for you, and tell me if you remember anything else about Cassie."

Fitz put the cigarette away unhappily. "She said her full name was Cassandra O'Brien," he said sulkily. "That's about it. We didn't really talk much."

Rose looked at the Doctor who was stroking his chin thoughtfully. "You know her?" she asked.

No, but that does not mean that it is insignificant," he answered. "However," he added in a slightly more optimistic voice. "The device has picked up her signature, and it will be easier to track her now."

Rose nodded. "Let's go then," she said.

"Steady on," said Fitz, looking at them like they were mad. "You are actually going to go after her?"

"Well, it is sort of what we do," shrugged Rose.

"The question is, do you want to come?" asked the Doctor, a smile playing at his lips.

Fitz was about to scoff and refuse, when he realised that this was looking rather like an episode of The Twilight Zone. He could be one of those handsome, dashing men who would crack the mystery and search out the truth. He nodded quickly and stood up. "Yeah, I'll go."

"Splendid," said the Doctor as the three of them left Molly's pub, Fitz waving gratefully at Molly as they passed. They emerged out into the cooling night air and glanced around. The street was all but deserted, except for a few stragglers swaying drunkenly around.

"Don't worry," Fitz told Rose when she glanced around a bit apprehensively. "I'll protect you."

Rose stared at him and gave an unlady-like snort. "Does it look like I need protecting?" she asked, raising her eyebrows as if daring him to contradict her.

"Got it," interrupted the Doctor, looking up from the tracking device. "This way, come on."

Rose shook her head at Fitz and picked up her pace to follow the Doctor, only to run into him when he stopped in the alley behind the pub. "What is it?" she asked, the darkness making it harder for her to see.

"Hang on," said Fitz, pulling out a matchbox from his jacket and lighting a match. "Jesus Christ!" he yelled, dropping the match when he saw what the Doctor was bending over. "Is that who I think it is?" he asked, his voice going high with fright.

"I am afraid so," said the Doctor. "The body was too weak to sustain the transplant, even if someone made very sure to prepare her the best way they could." He sounded furious and Fitz flinched as a cold shiver passed down his spine.

"There's someone there," said Rose suddenly, looking further down the alley. Before either the Doctor or Fitz could stop her, she was off running in that direction.

"Rose!" called the Doctor, looking up from his examination of Cassie's body.

"I'll go after him," they heard her reply faintly before she jumped over the railing and landed on the other side of the street. The Doctor gritted his teeth as he turned to Fitz. "Stay here, I'll go after her," he said.

"No way," said Fitz at once. "I ain't waiting with a dead body. Nuh-uh."

"Fine, come along then," said the Doctor as they started running in the direction that Rose had gone. Fitz was only too happy to get away from the body. But by the time they had jumped over the railing and come out on the other side, Rose was nowhere to be seen.

Rose crouched in the shadows as she watched the thin, grey-haired man enter one of the houses on the quiet street. She had made sure that he hadn't seen her while she had been tailing him all the way from the pub alley.

She knew that the Doctor would be furious at her for running away but this was their only chance to find the people responsible for doing that to the poor girl lying dead in that alley. Rose had to swallow back her revulsion as she remembered the cloudy eyes and the red lesions on her skin, not to mention the way she had been thrown away like trash in a urine-soaked alley.

Waiting for a few minutes, she gathered her wits about her and came up with a plan. She had to see who that man was and what they had in that house. If that transplant device was used recently, it was very likely that it was still there. Deciding to err on the side of caution, she sent off the address to the Doctor on the phone she had insisted that he needed to have ever since they had been in this universe. She emerged from the shadows and quickly patted her hair down as she went over to the house and knocked softly.

The door was opened by a woman in her late-fifties, wearing an old-fashioned black dress. "Good evening," said Rose with her most charming smile. "I am sorry to bother you but I appear to be lost. Would you happen to have a phone that I could use?"

The woman appraised her quietly before a wide smile appeared on her face. "But of course, my dear," she said in a sickly sweet voice. "Such a beautiful girl, all alone at a time like this. Come in, come in. I would be delighted to help."

A/N End of Part 3. Thanks for reading.

So, what did you think? We got more on Cassie and what's going on in good old London town.

How are you guys liking Fitz? I admit I was a bit reluctant to include him but I am having fun writing him so far.

The final part will have them dealing with Cassandra. It will be up soon. See you then!

~ Phoenix