Disclaimer: Doctor Who belongs to the BBC. I do not own any of it, nor do I make any money from it.

A/N Thanks for all the reviews on the last chapter. Here, is the final part and the killer is finally revealed.

Happy Reading!

The Space Mystery: The Reveal

Previously

The Doctor left Valerie at the door of the dining car and was turning around to look for Rose and Rory when he heard a faint sound. His brow furrowed as he realised that it was coming from the core to the Key to Time. The Doctor drew it out of his coat and held it in front of him.

The signal was no longer pointing to the luggage car. The Doctor followed the sound and it became louder when he came to one of the compartments. He tried the door but it was locked. Using his sonic screwdriver, he entered the compartment.

The core got louder and the Doctor moved the pillow aside to find the ornate dagger covered in blood lying on the bed. The Doctor did not touch the core to the dagger, knowing that he needed the proof before he could revert the key back to the original form. He tucked the core back into his coat and used a handkerchief to lift up the dagger.

He knew whose compartment this was and his suspicions were now confirmed. He knew exactly who the killer was.

In the dining car, all the first class passengers, including the Doctor's companions and Carter sat at a circular table. The Doctor was the only one not seated. He was circling the table slowly, his hands clasped behind his back.

Rory was beginning to get nervous. The Doctor's demeanour was calm and his face was so expressionless that it was unnerving. He had walked into the dining car ten minutes ago and ordered everyone to sit down. He hadn't spoken a word since.

He looked at Amy who was seated on his right and realised that she too was tense and looked ready to spring. He had shown the grey ash to the Doctor and he had given it a quick sniff before nodding but hadn't elaborated. Amy met his eyes and he recognised the questioning look. She wanted to know what the Doctor's game was. Rory shrugged at her and nodded towards Rose.

Rose was at Amy's right, and she was looking just as restless as them. She saw Amy's questioning glance and shrugged. The Doctor was making everyone nervous with his quiet pacing. Neither of them had any idea. It was Kramer who broke the silence.

"What is going on?" he demanded finally.

The Doctor stopped in his pacing and met Kramer's gaze. "I do apologise," he said pleasantly. "I tend to lose track of time when I am with my thoughts. You know how that must be." At Kramer's incredulous look, he tilted his head. "No, I don't suppose you would."

Kramer evidently gathered that he was being insulted and began to rise furiously from his chair. "Now look here..."

"The purpose of us gathering here," the Doctor spoke loudly over him. "Is to find out who killed Faber Bonasera."

"Did you find out who the murderer is?" Janelle asked eagerly.

The atmosphere at the table became even tenser, if that was possible. The Doctor nodded slowly. "The killer," he paused, injecting as much disgust as he could into the word 'killer'. "The killer is at this very table."

"Outrageous!"

The Doctor raised an eyebrow at Valerie. "Do you really think so?" he asked her critically.

Valerie opened her mouth but then closed it again. She had evidently remembered that there was a priceless dagger missing.

Watching her fall quiet, the Doctor proceeded. "Mr. Bonasera was killed with a single stroke of a blade. He bled out. But the question is, who wanted him dead?" The Doctor paused. "Rory."

Rory jumped slightly. "W-What?" he asked nervously.

"What did Mr. Bonasera say when he came to you?" asked the Doctor.

Rory looked slightly relieved before answering. "He asked for our help. He said he was in danger."

"Precisely," said the Doctor. "What would have put such fear in a man as ruthless as Mr. Bonasera was reputed to be? The answer, of course, was that someone had threatened his life. And the threat was severe enough for him to worry about. When he came to seek help from us, the killer panicked and took refuge in Faber's compartment."

"So when Faber went back in, the murderer killed him," said Rose. "But then how did the killer escape? We were right behind Faber and the door was locked."

"Always asking the right questions, Rose Tyler," said the Doctor, smiling at her. "Amy, what do you think? How did the killer escape?"

Before Amy could answer, Kramer made a sound of displeasure. "What is this, 'show and tell'?" he demanded. "Get on with it."

The Doctor glared coolly at him. "I will," he said. "In my own time. Amy?"

"I don't know," said Amy, honestly.

"Do you know what? I don't either," said the Doctor and everyone gaped at him incredulously. "But I suppose we should simply ask the killer. Dr. Greenfield, if you will."

Tristan stared at the Doctor. "What are you on about? I don't know," he said indignantly.

"Oh come now," said the Doctor, his gaze cold as he looked at him. "I know you killed Faber."

"This is preposterous!" yelled Tristan as he jumped to his feet.

The Doctor glared at him. "Faber was suing you for negligence during his wife's surgery. He was one of the best attorneys around Snowdell and he would have been successful. And you would have been penniless and completely ruined."

"Alright yes, but I did not kill him!" shouted Tristan.

"After supper, you followed him to the luggage car and told him to withdraw his case or you would kill him," continued the Doctor mercilessly. "Faber had been drinking and was unstable which meant that he panicked and rushed to Rory for help. You had no choice, you had to run. So, you hid in Faber's compartment and killed him when he came in."

"You're just spinning wild tales," yelled Tristan. "Where's the proof?"

"Ash," said the Doctor. "From the cigars you have been smoking. I found traces in the luggage car as well as outside Faber's compartment. And then, there is the murder weapon." The Doctor pulled out the dagger wrapped in the handkerchief and placed it on the table.

There were gasps from almost everyone as they saw the blood-soaked dagger. Tristan stared at in horror. "I have never seen it before," he said, looking pale.

"It originally belonged to Valerie," said the Doctor, inclining his head towards her. "But you stole it when Faber ran to us. You didn't count on the alarm being raised so quickly which was why you did not have time to hide the weapon. I found this in your compartment," he said, glaring at Tristan.

"Someone is setting me up!" yelled Tristan. "I did not kill Faber Bonasera!"

"Oh no," said the Doctor ruthlessly. "You were the one who was doing the setting up. You grabbed the first piece of clothing you found in the luggage car which happened to be Janelle Lombardi's kimono which she had packed in her bigger luggage at the last minute. You thought that if I found that, I would suspect Janelle rather than you."

Kramer put a protective arm around Janelle as she gasped and stared at Tristan in horror.

"This is not true!" Tristan shouted.

"Enough," said the Doctor coldly. "If you won't confess and tell us how you escaped, then we'll just arrest you now and you can confess when we get to Applepond. Amy, if you will."

Amy stood up and pulled out a pair of handcuffs from her purse. Tristan was staring at the Doctor in horror and disbelief as Amy handcuffed him. "You are making a mistake," he said, his voice shaking. "I am innocent."

The Doctor watched him in disgust. "Get him out of my sight," he said. "Lock him in one of the compartments."

Rory jumped up to help Amy as they led Tristan out of the dining car. The Doctor grimaced as they disappeared down the corridor. "That's the end of that ghastly business," he said. He looked at the remaining passengers. "Don't worry, I'll make sure Tristan talks about how he got out of Faber's compartment. He will pay for his crime."

Janelle and Kramer nodded while Valerie was still staring at the dagger. "It has been in the Richmond family for centuries. Now, it is ruined," she said mournfully.

"Don't touch it," said the Doctor when she extended her hand towards it. "That is evidence."

"Surely, Doctor," began Valerie but the Doctor shook his head.

"I'm sorry, Valerie," he said, picking up the dagger still wrapped in the handkerchief. "No one touches it." As he lifted the dagger away, the tip of the blade grazed Keira Richmond's arm and an angry red welt appeared on her skin for a moment before vanishing.

She realised that her game was up the same moment that the Doctor dropped a blue energy cell around her, trapping her inside. She reverted into her original form and let loose a shriek of anger.

"What the hell?" Rose yelled, looking at 'Keira'. "What is she?" The pretty brunette had transformed into a creature with a long grey body, limp green hair and vicious red eyes. Her mouth was open and sharp, pointy teeth were visible as she snarled at them.

"A siren," said the Doctor grimly as he watched her yell and scream inside the energy cell. "A creature of chaos."

"That is not..." Valerie sounded faint. "My granddaughter. What has happened to her?"

"I'm sorry, Valerie but I'm afraid your granddaughter never left Snowdell. The siren was impersonating her," said the Doctor, gently.

"Is she...my real Keira...is she okay?" Valerie asked, still staring horror-struck at the thrashing siren.

"Yes, I should think so," said the Doctor.

"How-how did you know she was a siren?" asked Kramer, holding a distressed Janelle close.

"I didn't know for sure until I had finished interviewing everyone," said the Doctor. He saw Amy and Rory re-entering the dining car, looking upon the scene in horror and surprise. "Ah, Amy, Rory, if you could release Tristan, I assure you he is quite innocent."

"Tristan did not kill Faber then?" Rose asked.

"No, of course not," said the Doctor gently. "The man is many things but a killer is not one of them. Tristan," he said to the recently freed man who looked shocked. "I apologise for putting you through that ordeal. But I had to make the siren lower her guard to trap her."

"What's a siren?" Tristan asked, aghast.

"It's a creature that feeds off chaos," said the Doctor. "They trap and beguile people, and once they are under their submission, they feed off their life force until they die."

"A parasite then," Rory realised.

"Of the worst kind," the Doctor agreed, glaring at the siren who was now hissing at him angrily.

"She must have latched onto Faber then," said Amy.

"She did," nodded the Doctor. "But Faber broke through the spell. Remember he seemed so guilty during supper? He was feeling guilty for failing his wife and getting close to another woman so soon after her death. That's why he was leaving Snowdell behind. Guilt," said the Doctor softly. "It's a very powerful emotion."

"That's why he was so hysterical when he came to us," said Rory. "He realised what the siren truly was."

"But why kill him?" asked Rose. "He couldn't have harmed her."

The Doctor stared at the siren's red eyes. "It's because of me, isn't it?" he said. "You knew who I was and what I would do if I knew who you were."

"Yes, I know who you are!" hissed the siren angrily. "Interfering Time Lord of Gallifrey. You would have killed me the minute you knew who I was."

"How did you know?" asked Amy.

"During supper, I noticed that 'Keira' was left-handed," said the Doctor. "Later at the end of our interrogation, I threw my screwdriver at her and she caught it in her right hand."

"So?" asked Kramer.

"She hurt her left hand when she used the dagger to kill Faber, just like when the tip touched her just now," said the Doctor as he held up the dagger. "Maridium is harmful to sirens. Just a single touch can be toxic and prolonged contact can kill them."

The siren was staring at the dagger in fear as if expecting to be impaled by it. Rose turned to the Doctor. "What about the cigar ash? And Janelle's kimono?" she asked.

"Like I said before, it was to cause confusion," said the Doctor. "The siren thought the blame would get pushed onto one of them. Most likely to Tristan since she left the bloodied dagger in his compartment."

"But she had an alibi," Rose pointed out.

Janelle, who still looked quite shell-shocked, nodded. "She was with me the whole time. We drank wine and caught up on girl talk."

Rose stared at her in horror. She had repeated herself almost word for word. The Doctor glanced sympathetically at Janelle. "I am so sorry," he said. "She put you in a trance. That is why you have been having so many mood swings. It's your mind trying to fight the siren's influence."

Janelle burst into tears and Kramer looked at the Doctor helplessly. "How can I stop it?" he asked.

"She will heal," said the Doctor gently. "Given time and care." Kramer nodded and held her closer.

"How did she escape from the compartment after killing Faber?" asked Amy finally.

"Sirens are powerful creatures," said the Doctor gravely. "They can transform themselves into literally any physical form. She could have made herself invisible and slipped past us."

The siren looked a bit put out which made them realise that the Doctor had been right in his guess. "What do we do with her now?" asked Rory.

Fear flashed across the siren's face as she looked at the dagger that the Doctor was holding. "I'm not going to kill you," said the Doctor, guessing her look. "I happen to know an excellent prison in the Prism galaxy that houses sirens. We'll simply take you there."

The siren began to laugh loudly. The horrible sound raised the hairs on their arms. "Captivity?" she asked. "You grow weak in your old age, Doctor."

"Not really," he said sadly. "Just more merciful."

"Your mercy means nothing to me, Time Lord," she hissed. "I have failed my purpose. And now I shall die."

The words caught up to the Doctor but before he could deactivate the energy holding cell, the siren had drawn out a vial of milky liquid from her dress and downed it quickly. "NO!" the Doctor yelled but the siren smiled mockingly at him and fell to the floor, dead.

The stunned silence was broken when the train came to a stop. "We're here," said Carter who had been silent the whole time. "We're at Applepond."

The return train from Applepond to Snowdell did not leave for another two hours. The Doctor and his companions had bidden a hasty retreat once the train had got to Applepond, knowing that the Doctor was not really Inspector Smith. Rory felt a bit guilty about leaving such a huge mess behind but the Doctor assured him that human beings were good at coping and they would be sure to come up with a proper story to explain the bizarre events onboard the Orient Express.

At the moment, the Doctor and Amy were seated at a table in a small cafe while Rose and Rory fetched some food and drinks for all of them. Amy had been quiet the whole time but when they were alone, she leaned in close. "You heard what the siren said, didn't you? She said she failed her purpose."

"Yes I did," the Doctor said, looking thoughtful. "But I didn't think you did."

"I had heard about sirens," said Amy, not taking offence. "They are creatures of chaos, like you said. Maybe even an agent of chaos."

The Doctor glanced at her with shrewd eyes. "Well done, Pond," he praised. He looked back towards the counter where Rose and Rory were placing their orders and lowered his voice. "I do agree that the siren could have been sent by the Black Guardian."

"He is not messing around, is he?" said Amy, trying to keep her tone light.

The Doctor did not smile. "Yes, the White Guardian did warn me about it. We should be more careful from now on," he said. "Keep this between us for now," he added hastily as he saw Rose and Rory returning to their table.

"Hey, what're you guys talking about?" Rose asked as she and Rory sat down.

"Nothing, just the usual," smiled Amy casually.

"So, what happened to the segment of the Key?" Rory asked. "Did you actually find it?"

"Ah yes," said the Doctor as he drew out the dagger from his coat.

"How'd you manage to steal that?" Rose asked. "I would have thought that Valerie would have demanded it back."

"She was a bit distracted after the events," said the Doctor. "And rather eager to check up on her real granddaughter."

"That is the segment, is it?" Amy asked, looking at the dagger.

The Doctor smiled as he placed it on the table and then touched it with the core to the Key to Time. The dagger shimmered for a moment before transforming into the second segment of the key. With a satisfied smirk, the Doctor tucked the core and the segment back into his pocket. "See," he said. "Easy as ever."

His companions chuckled at his proclamation. Easy had nothing to do with the quest to the Key to Time. But they admired his optimism.

"Two down, four to go," said Rory as they began to tuck into their food.

A/N End of #2 The Space Mystery. What did you think?

Despite various variations of 'Sirens' in Doctor Who, there haven't been proper sirens in the show. 'Curse of the Blackspot' siren was a nurse and 'The Sirens of Time' are very different creatures but similar in some aspects. So, the alien is sort of a hybrid made from various canon and non-canon myths.

The next story is called 'The Gogan Colonisation'. It sees an old enemy of the Doctor making an appearance. They appeared only once on screen during the First Doctor's era but were recently mentioned as being a part of the Pandorica Alliance during 'The Pandorica Opens'.

Part 1 will be up soon. Let me know how this one was.

~ Phoenix