Warrick Brown, meanwhile, was preparing to speak to the mysterious Rose Tyler, who appeared to be very much alive despite the fact that they had arrested her murderer. Nick Stokes sat beside him, the speaker phone on the table in front of them. The phone rang five times, before a young woman's voice answered, "Hello?"

"Hello, this is Warrick Brown, I'm with the Las Vegas police department. I'm here with Nick Stokes. May we please speak to Rose Tyler?"

There was a shout in the background, and the woman put her hand over the phone. "Mum, it's the police. I don't know what they want, they sound American. Well, how the bloody hell should I know? It's not like I've ever been out of the country." She then spoke back into the receiver. "Yeah, Rose Tyler, that's me."

Warrick looked over at Nick. Neither of them had really expected to speak to her. Warrick continued in a steady voice. "Miss Tyler, it appears that you took a trip to Las Vegas three months ago?"

Rose laughed. "Um, three months ago I was in school. I'm pretty sure they'd know if I skipped out to go to Las Vegas."

"In school," said Warrick. "In London."

"Yeah," said Rose. "Never been to Las Vegas."

Nick leaned over to talk more directly into the speaker phone. "Miss Tyler? Nick Stokes. It is very important that you tell us if you've been in contact with a tall man, looks to be in his forties, no hair, big ears, with a northern accent."

Rose appeared to give this some thought. "I don't think so," she said. "Hang on." She shouted, "Mum! You been seeing any guys, mid forties, bald, northern accent?"

An incomprehensible yell back seemed to answer her question. "Yeah," said Rose. "We haven't seen him. Why? Did he mention me?"

"We just think that you should be careful," said Warrick. "We think you might be in a certain amount of danger."

"How about a very tall, thin man, early thirties, wiry frame, brown eyes, spiky hair, calling himself the Doctor?" asked Nick.

"No," said Rose immediately. She giggled a little bit. "Not sure why you think I've got tons of men around me all the time."

"In all honesty, Miss Tyler," Warrick said, "this really isn't a joke. We think you might be in serious danger."

Across the room, the door opened and Sara stuck her head in. She looked upset, her mouth in a frown, her eyes curious. "Ask her if she knows what a Sonic Screwdriver is."

Warrick and Nick looked at one another. Nick coughed. "I'm sorry to bother you again, Miss Tyler. But do you have any idea what a Sonic Screwdriver is?"

"Um," said Rose. "Orange juice and vodka? No, wait, that's just a screwdriver." She paused, then shouted, "Mum! What's in a Sonic Screwdriver?" Once again came the indecipherable shouting. Rose got back to them, "yeah, we're pretty sure they don't have that in London. But Mum thinks it's just like a normal screwdriver with lemon."

Sara shook her head. "She doesn't know anything, you guys," she said. "Wrap it up." And closed the door.

"We're sorry to waste your time, Miss Tyler," said Warrick. "Thank you very much for answering our questions."

"Yeah, no problem," said Rose. "And I'll be on the lookout for creepy men with northern accents and sonic screwdrivers."

Of course, two years later, Rose would forget the entire conversation.

"So this is what the tapes are for," said the Doctor. "They're for the police to find when my body is on the autopsy table."

"Do you think that there is someone trying to murder you?" asked Dr Bradshaw.

"You, apparently," said the Doctor. "At first I thought you just wanted to get into the Tardis, but I'm pretty sure that choking me for three hours was not a method of extracting information."

"We are trying to keep you hydrated and fed, Dr Smith," said Dr Bradshaw. "If you would eat voluntarily, your life would be far easier."

"Or maybe," said the Doctor, "you aren't trying to kill me. Maybe you're just curious. Never seen an alien before, want to see how I tick. How long I can go without air. How much poison you need to pump through my body before I go into cardiac arrest."

"Are you telling me that you are an illegal alien, Dr Smith?" Dr Bradshaw asked.

"Oh, I'm sure you know that," said the Doctor. "Illegal alien. In every sense of the term. Just your own personal lab rat."

There was a pause. Then, quietly, "Do you deserve it, Doctor? Don't you think you deserve it? For Gallifrey?"

The Doctor said nothing for a long time. "Yes," he said. "But not from you."

Nick gave a triumphant, "ha!" when he found Sarah Jane Smith on the computer. "Found her. Sarah Jane Smith. Independent journalist, living in London." He checked his watch. "I don't think we'll wake her up if we call right now."

Warrick hesitated. "You know," he said. "The vic did leave us that message knowing we'd contact her. You don't think it's some kind of trick?"

Nick considered this. "Probably," he admitted. "But I'd say we hunt down every lead we have so we can figure out a little more about who this Dr Smith really is and why it is that all the people on his body count list are either still alive, or died about a hundred years ago."

Warrick considered this, and decided it made a certain sort of sense. He was still a bit baffled that Rose Tyler had been unable to tell them anything useful. After all, she clearly knew the vic, and she clearly knew the vic's friend. That much had been obvious from the surveillance footage. But Sara had told them that if she didn't know what a 'sonic screwdriver' was, she didn't know anything.

"I think it's a sort of codeword," Sara had explained to them. "It's certainly the reason he told us to be weary of the police. When I mentioned it to them just now, they clearly recognized the term. I think it's like, if you know what a 'sonic screwdriver' is, it means you know who the Doctor is. And since I haven't a clue about the screwdriver, I guess that told him something."

So they called up Sarah Jane Smith on the speaker phone and waited as the phone rang. Nick checked his watch again. They were calling fairly late, considering the time difference, so he wouldn't be surprised if she didn't pick up.

He didn't realize he'd been holding his breath until he released it when a woman's voice answered the phone. "Hello?"

"Hello, this is Warrick Brown and Nick Stokes with the Las Vegas crime lab, and we were hoping to speak to Sarah Jane Smith."

"Speaking," the voice on the other end replied. It was an elegant, deep voice, with a clear English accent. Not that either of them had expected any different from someone who lived in London. "I'm sorry," said Sarah Jane. "Did you say you were calling from Las Vegas? From the United States?"

"That's correct, Ma'am," said Warrick.

On the other end of the phone, Sarah Jane gave a small sigh. "I don't suppose this is about a man in oddly dressed clothing who chases trouble, speaks nonsense, constantly bombards strangers with offers of jelly babies and stubbornly insists that his name is just 'the Doctor'?"

Warrick and Nick looked at each other. "Yes," said Warrick carefully. "I assume this means that you know him."

"Listen," said Sarah Jane. "I know why you're calling, and trust me, you've got the wrong man. The Doctor wouldn't harm a fly. In fact, if he's around, he's probably trying to save the world, and all you're doing by locking him up is making his job more difficult. I've got sources, people you can call. Authorities. Just keep in mind that if the Doctor's shown up, that means things are really, really bad."

Nick cleared his throat. "Actually," he said softly, "I think you've misunderstood. The murder we're investigating… your friend isn't a suspect. He's the victim."

"You mean he's dead?" Sarah Jane asked. She didn't seem upset. She just sounded a little annoyed. "Well, that's just ridiculous. Just wait a while. You'll see."

"I'm sorry," said Warrick, "but your friend is definitely dead. His body is in the morgue, and we checked all his vitals. His heart has stopped, his breathing has stopped, his body is cold. He is definitely dead."

"How long has it been?" demanded Sarah Jane. "When did he die? How long did you wait?"

Nick checked the clock. "Nearly 12 hours," he said.

Sarah Jane gave a sudden sharp intake of breath. "His body!" she cried. "His body. It was stolen, wasn't it? That's why you're calling. He was in the morgue but then his body was stolen and you're trying to figure out who took it."

Warrick and Nick exchanged another look. They had heard people desperate not to believe that their friends and family were actually dead, but they really were not expecting it to go this far. "His body is still in the morgue," said Warrick. "We're legally required to perform an autopsy in these situations. I'm very sorry for your loss."

Sarah Jane said nothing for a moment. "His body is still there," she said in a much quieter voice, "looking exactly the same as when you last saw him?"

"Yes," said Warrick.

"He hasn't just… turned into someone else and walked off?" Sarah Jane asked.

"No," said Warrick.

Sarah Jane paused, and for those precious few seconds, Warrick and Nick thought they might have finally gotten through to her.

"Then it's not him," said Sarah Jane. "If he didn't regenerate, it's not him. You've got the wrong guy. It isn't him!"

"Does the phrase 'sonic screwdriver' mean anything to you?" Warrick prompted.

"So he stole the Doctor's screwdriver!" Sara nearly screamed at them. "That doesn't make him the Doctor. Because the Doctor isn't dead. I'd know if he was dead, and he isn't. He can't be."

"If it helps," Nick told her, "he left you a message."

Warrick gave him a questioning look. He wasn't really sure this was a good idea. But Nick seemed set on it. He took out the tape, popped it into a tape player, and played it for Sarah Jane.

By the end, they could both hear her sobbing. They knew then that they'd gotten through to her. Something in that message must have proven to her beyond a shadow of a doubt that he was really gone. They kept trying to offer her words of comfort, but she didn't seem to hear.

When at last the sobs had subsided, she finally managed to ask, "where's the Tardis?"

"The what?" asked Warrick.

"The Tardis—the blue box he told you to take care of," said Sarah Jane. "Where is it?"

"We didn't find it," said Warrick. "It was gone when we got there."

Sarah Jane gave a small sniffle, but then seemed to pull herself together. "I want to speak to Sara Sidle," said Sarah Jane. "Alone."

Nick and Warrick exchanged glances once again, but Nick reluctantly got up and went over to the door. "I'll see what I can do."

After he left, Warrick kept prodding Sarah Jane for information, but she was stubborn. "I'm only talking to Sara Sidle," said Sarah Jane. "The Doctor said he trusted her, and I trust the Doctor. As far as I know, she's the only one of you who isn't some evil bug-eyed alien trying to take over the world."

Before Warrick could figure out what she meant by this, Sara entered the room. He got up, and offered Sara the seat in front of the speaker phone. She took it, graciously.

"Hello, Miss Smith?" she said. "This is Sara Sidle from the Las Vegas crime lab. I was told that you wanted to speak with me?"

"Are the others out of the room?" asked Sarah Jane.

Sara Sidle looked at Warrick and Nick, who were still hovering over her. She made shooing gestures at them until they buggered off. When the door closed, she turned back to the speaker phone. "Yes," she said. "Now we're alone."

"Keeping things between us Saras," said Sarah Jane. She gave a sad sigh. "Look, if the Doctor's dead, and he left you a message, he did it for a reason. There's something terrible going on, Sara, otherwise he wouldn't be here. He only shows up to stop terrible things from happening. It's what he does. I heard the message he left you, and I think I know what I'm supposed to tell you."

"You think he set this all up just to get me to do something?" asked Sara.

"I know he did," said Sarah Jane. "Listen, Sara. You've got to find the Tardis. There's something very, very bad out there, and it wants the Tardis. I don't know why he downplayed it on the recording—I guess he thought someone was listening. But find the Tardis and guard it with your life."

"The what?"

"The blue box," said Sarah Jane. "It's a police box from the 1960's. Someone's taken it, and like he says, whatever they want it for isn't good."

"I'm confused," admitted Sara. "If he's just trying to manipulate us, why should I try to do what he says?"

"Because he's the good guy," Sarah Jane told her. "I know you probably think he's crazy, but he's not. He has a list of enemies about a mile long because he doesn't believe in killing people, no matter how evil they are. And I've seen him. I was there, when he was asked to destroy the beginnings of the most evil race of creatures in existence. He couldn't do it. He's a good person, and you have to trust him, or else everyone on this planet is going to die."

"What… how…" Sara couldn't form her thoughts into a question. This whole case seemed really familiar, but she couldn't put her finger on how or why. "Who are you?"

Sarah Jane gave the other Sara a brief rundown of her history with the Doctor. "And I know you don't believe me," said Sarah Jane, "but you will as soon as you start questioning the people around you. I think you're dealing with some sort of mind parasite. They get inside your head and control you, and the longer they're inside, the less of you there is left. As soon as they figure out that you're working for the Doctor, they'll try to get you, too. In fact, they may have already gotten into the people closest to you."

"Wait, hold on a second," said Sara. "You sent Warrick and Nick out of the room… are you saying…?"

"Don't trust anyone," Sarah Jane told her. "Don't trust the people you know, don't trust your friends, your family, anyone. The Doctor—he had all these little tricks he used to use to figure out whether people were really themselves or not. I wish I could remember them."

"I remember," said Sara. "He used those tricks on me. Kept quizzing me on history and common idioms."

"Yes," said Sarah Jane. "Do that. Make sure that the people are who they say they are. Just do what the Doctor says, and stay in groups. I don't know why, but I'm sure he had a reason."

Sara considered this. "Would you be willing to come out and identify the body?"

Sarah Jane laughed. "I couldn't if I tried," she said. "He looks different every time I see him. But I'll tell you what. Open him up and look inside. If he's the Doctor, you'll know, because he won't look human. He won't look human at all."