Grissom hung up the phone. "Backup is on the way," he told Sara. He looked down at Verity's body. "From a preliminary examination, I see nothing that would indicate foul play. No external lacerations, no discoloration, no entry or exit wounds…"

"Just before she collapsed she showed symptoms of illness," said Sara. She leaned against a desk, folding her arms. "Profuse sweating, uncontrollable shaking, dilation of the pupils. Heart failure, perhaps?"

Grissom fished into his bag and pulled out two pairs of rubber gloves. "I'll leave that for autopsy," he said, putting one pair on his hands. He offered the other pair to Sara. "In the meantime, it appears that this has now become a crime scene. Which means that we have work to do."

Sara got to her feet with a sigh, and took the offered gloves. "This is just like the Case that Never Ended," she muttered.

Grissom was about to ask Sara what she meant when they both heard a sudden "click" sound echo through the room. They both looked at one another for a moment. Sara could have sworn it sounded like… a tape recorder? She looked around the office. The surveillance footage and the prisoner files had all been digitized. Who still used audio cassette tapes?

It was Grissom who found the tape recorder. It was an old model, a large black rectangle of metal and plastic with a tape still inside. Grissom dusted the box for fingerprints, and looked back at Sara, surprised. She went over and looked over his shoulder, but when she saw what he'd discovered, she gave a bitter laugh.

"Oh, that is just not fair," she said.

The box was covered in fingerprints. Every surface was filled with them. And every set appeared to be different.

"Apparently, someone figured out that we'd do this," said Grissom.

"Apparently," Sara corrected, "Verity Cordman was paranoid enough to record our conversation."

Grissom considered this, then rewound the tape and pressed play. The recording began with nothing but the background hum of the computer. There were footsteps, but they were not the sharp tap of Verity's heels. So, not Verity. Sara heard a door open and close, very quietly, as if the person who had placed the tape recorder had snuck in. For a few minutes, the recording was silent. Finally, a woman's muffled voice could be heard. Verity Cordman. She must have been outside the door. They heard the door open, and footsteps enter. Verity was humming, her voice now clear through the speakers.

There followed a long period of near silence, save for occasional sounds of coughing, typing, humming, or footsteps. It was during this period that Sara's phone began to ring. She waved to Grissom, walked out of the office, and answered it. "Sidle."

"Yeah, it's Greg," said the voice on the other end. "And I just want to tell you to stop jinxing my machinery."

Sara looked at the phone, as if it was to blame for the sentiment. "What?"

"About three months ago, you gave me this DNA sample, and every time I ran it through the system, the whole thing went nuts," said Greg. "You know the drill. Program freezes, computer blue screens, and suddenly, I'm calling IT and spending my lunch breaks trying to catch up with all the work I'm not able to do. Three months later, same thing happens, and guess what I find out? It's another one of your cases. So I don't know what kinds of samples you keep sending me, but really, if they're not biological, send them to trace."

Sara could hear the protests coming out of her mouth before her brain had processed the information Greg had given her. As soon as she had worked it through her mind, however, she stopped talking. "Hang on, three months ago?"

"Yeah, near enough," said Greg.

Sara felt her blood run cold. "It's the same guy," she said.

"Huh?"

Sara had begun pacing in the hall outside the door. Her hand was clutching the phone. "Greg, tell me something. Three months ago, the DNA evidence under Katherine Marshal's fingernails. Did that sample break the machinery?"

"Let me check. Hang on."

There was the shuffling of papers on the other end of the line, and Sara scarcely allowed herself to breathe. She had a terrible feeling about this, and she was hoping beyond hope that her intuition was wrong.

"Yeah, got it," said Greg. "Sorry about the delay, but the computer's down. But I guess you already knew that."

"Greg," Sara cut in. "Please, just tell me."

"Um, nope," said Greg. "Just a simple negative ID, no match found in the database. Didn't scramble any computers."

"Oh, no," Sara breathed. For a moment, all thoughts ceased in her brain, all background noises seemed to fade away to silence, and she could only feel the rhythm of her heart beating in her chest. She was falling, falling into nothing and she didn't know if there would be anyone to catch her.

"Sara?" came Greg's voice on the other end of the phone. "Are you okay?"

"I killed him." The words were coursing through her veins, pulsing through her fingers, tingling in her toes. They leaked through the pores of her body, spilling from her lips, ringing in her ears, scratching at her nose and congealing in her eyes.

The door to the office opened and Grissom came over. She could hear him as he spoke her name. She could feel his hands on her shoulders—those soft, gentle hands that gave her back a touch of the warmth she thought had deserted her forever. She turned around to face him, and again felt the words leak off her tongue. "I killed him."

Grissom eased the phone from her hand, and held it to his ear. "Greg? It's Grissom. Yeah, she'll be fine. She'll call you back." He hung up the phone, and looked deep into her eyes. "I think you should probably hear this," he said, and led her back into the office.

"The side we were listening to was essentially blank," Grissom explained. His voice was more gentle than usual, and Sara could hear it echoing through her mind as she desperately tried to grasp the words. Grissom bent down and began fiddling with buttons on the tape recorder. "Until we entered, that is, but we already heard that part. But then I thought, since Verity was not the person who set up the recording, who did? And what would their motivation be for doing so? Maybe this was just a way to get our attention, and the real message was on the other side of the tape. So I turned the tape over, and…" he shrugged. "Listen for yourself."

He pressed play.

"It's on," came an unfamiliar voice over the speakers. It was low and gruff, a man's voice, but clearly a man who wanted people to feel like he had a certain amount of authority. His words were short and clipped, and he sounded angry. ("Sammy," Grissom mouthed at her.)

"Hello," came a cheerful voice with a British accent. "I'm the Doctor. Not sure who's listening to this recording, but I'm pretty sure that if you're hearing this I'm dead. Not sure how dead yet. Hoping it's not dead for good, that sounds rather nasty. Still, better to live in hope."

The voice paused, and added, "Yeah, bad choice of phrase," as if he were responding to some gesture that Sammy had made.

"Anyways," the British voice continued, "I was hoping to talk to Sara Sidle. From the crime lab, if I remember correctly. Brilliant woman, very good at her job. Gold star! Do they still give those out anymore? Right. Yes. Sorry. Message. Sara Sidle, you've probably figured out by now that I didn't kill that woman. Just wrong place at the wrong time." He gave a sharp breath, and when he continued, his voice had lost that happy, rambling ease. It was softer, more serious, as if every decibel was prying into Sara's subconscious. "I just want to make sure that you know that this isn't your fault. I know what happens when you hold yourself responsible for the actions of others. I know how that guilt eats away at you, and leaves you hollow. So I'm asking you, please, to let it go. First off, I was trying to get here. When we met, I pretty much put a big sign on my head saying, 'send me to jail, please!' Second, I could have escaped dozens of times by now, as certain people keep pointing out to me."

Sammy's voice gave an annoyed grunt.

"And, as I keep pointing out to certain people," the British voice continued, pointedly, "there is someone or something in this prison that's in trouble and needs my help. I don't know what it wants or who it is, but it's prepared to kill a fairly large number of people in order to get me, and as long as I'm here, it isn't harming anyone else. I think it's safe to say that I've met it before, and it wants to extract some sort of revenge on me before it tells me what it really wants. So I'm staying until I can either work out some way to help, find some way to contain my past mistakes, or… well, until I die, which is looking more and more likely each day. I'm just asking you to do one thing in my honor. Keep fighting the fight. Keep stopping the violence, helping the weak, locking up the bad guys. If there's no more Doctor in the world to stand up for what's right, at least I know there's a Sara Sidle out there, helping keep the streets safe." He paused. "Message ends."

The recording went silent. Sara looked at Grissom, who looked back at her. "That was the guy I talked to before," she said. "John Smith. That's our vic."

Grissom nodded. He opened his mouth to speak again, then stopped, and examined her more closely. "Are you okay?"

Sara hesitated before answering. "I think so," she said.

"He's right, you know," said Grissom. "You shouldn't blame yourself. You did not withhold or manipulate information to facilitate a conviction. You didn't come at the case with any preconceived bias. You did your job."

"And he died because of it," said Sara.

Grissom didn't say anything, and Sara could see his face bending into that thoughtful countenance he always wore when he was trying to work out a case. He drummed his gloved fingers against the side of the tape player, absent mindedly. "There's something wrong about this whole situation," he said. "I can't put my finger on what it is… but I think we'll find the answers somewhere in this room."

Nick Stokes stood looking at the faded carvings along the walls of the cell. Most of it just looked like jibberish – circles and squiggles that followed no pattern or logic. But every so often, he'd find something recognizable. Not the intention, of course, because math had never been Nick's strong suit. But it was clearly some sort of complex mathematical equation, and unless Nick had just been swallowed up by the movie Good Will Hunting, he was betting that Sammy hadn't been the one figuring them out.

"Find something?" asked Warrick.

Nick spun around. Warrick Brown was beside the bars of the cell, looking like he'd just solved a very complicated puzzle.

"Go on," said Nick. "Impress me."

Warrick walked over and handed him the key. "Go ahead, lock me in."

Nick shrugged, took the keys from him, and complied. He looked through the bars at Warrick, who was standing inside the cell with that same look on his face.

"Okay, you're locked in," said Nick. "Now what?"

"Now comes the tricky bit," said Warrick. Warrick turned back to the bars, twisted his body sideways, and put pressure on two bars with his hands, another with his left foot, and one last bar with the top of his head. To Nick's complete surprise, the cell door popped open and Warrick walked right out.

"No way," said Nick. "Don't tell me that's some kind of design flaw and that prisoners have been able to do this for years."

Warrick walked over to the next cell, and Nick locked him inside. He tried the same stunt, with no success. "Apparently not," said Warrick.

Nick and Warrick went back to the first cell, and examined the bars more closely. "It appears that someone figured out the perfect pressure points and managed to weaken them," said Warrick. "Weaken any door at the right points, you damage the structural integrity, and the door'll open for you, no questions asked."

"Think that's what the markings on the wall are for?" asked Nick.

Warrick went over to the wall, and studied the recognizable mathematical symbols. "Yeah, that's it," he said. "But it's… confusing… like looking at a 3D graph in four dimensions."

Nick leaned closer to the bars and examined the filed markings. "Call me a skeptic, but I'm pretty sure Sammy wasn't the guy to come up with this. Mathematical formulas, pressure points, structural integrity… this sounds like something our Dr Smith would have come up with."

Warrick shrugged. "Might have explained why he liked to be called 'the Doctor.'"

Nick looked back at him, puzzled.

"You know?" said Warrick. "Bolster the ego. Make him feel smart."

"I figured he must have been some sort of drug dealer," said Nick.

"Sara didn't find any evidence of drug dealing when she worked on his case," said Warrick. "Doesn't rule it out, of course. But you know what Grissom would tell you. Stick to the evidence."

Nick was about to reply, when he was interrupted by a loud, clear "click". Nick and Warrick both jumped at the sound, surprised, then began looking through the cell.

"It came from somewhere along the back," said Nick. He was fishing around by the wall, trying to find some sort of hidden area. "Aha!" he cried, and pulled out a chunky, black tape recorder.

The first thing they noticed was that it was an old model, outdated, and still a little dusty. The second thing they noticed, after dusting the case for fingerprints, was precisely the same thing that Sara and Grissom had noticed back in Verity Cordman's office.

"Oh, you are kidding me," said Nick.

"Think that's all the prisoners?" asked Warrick, gesturing at the many finger prints.

"If they're smart, it'll be all of them," Nick replied. "Too many suspects, too much data, no conviction." He paused. "You think there's something on the tape?"

Warrick started to object, but then stopped, thought it through, and rewound the tape. There was nothing but the sounds of both their voices. On a whim, Warrick flipped the tape over, and tried the other side.

They were not expecting anything, so both of them jumped when they heard the voice.

"Hello," came a cheerful British voice. "I'm the Doctor. But I'm guessing you probably already knew that. And no, I'm not stalking you. That would be creepy. Especially since I'm a voice on a tape. Can you be stalked by a voice on a tape? I'm sure someone's made a movie about that somewhere. Then again, someone's made a movie about everything, so it would hardly be surprising. You should see the bazaars in the late 4300's. You just pull a word out of a hat and they have a list of movies about it. Absolute rubbish, most of them, but… oh, yes. Sorry. Message.

"This is a message for Sara Sidle from the Las Vegas crime lab. Brilliant, wonderful young woman, probably still assigned to this case. Anyways, if you're listening to this, I'm probably dead. Hopefully not for good, but, well, rest assured I've been getting warnings. You can say I've been expecting this for a while now. Haven't heard anyone knocking yet, but pretty sure that's coming soon. Right, well, better make this quick. Don't know when they're coming back, and," he cleared his throat, "some people really do need to get back to their cells and stop risking their lives to try to convince me to leave." He gave a small sigh. "Sorry, sorry. You're being terribly helpful. I really do appreciate it.

"Well, Sara, I know you're an intelligent young woman, and you've probably worked most of this out for yourself. But just in case you haven't… please, watch out. Keep your eyes open. There's someone in this prison who is really very dangerous, and despite my best efforts, I don't see how I can contain him. I'm trying my best to help him, and sometimes I think I might be getting through, but to be honest, I'm not sure if I'm doing any good. If I'm dead, which seems quite likely given that you're listening to this tape, I honestly don't know what he'll do. So keep your eyes and ears open, and don't trust anyone, even if you know them. Don't trust the people running the prison, don't trust the staff, don't trust the warden, and definitely, definitely, don't trust the police. They may look like your friends, Sara, but appearances are not everything. There's something terribly evil in this prison and it knows who I am. And if it knows who I am, and wants me out of the way, then whatever it's got planned can't be good."

The voice paused a moment on the other end of the recording. "Oh, and not to bias your investigation or anything, but I'd look in the basement if I were you. Just a hint. Message ends."

Nick and Warrick looked at one another for a moment. They suddenly had shivers going up and down their spines. Nick ejected the tape, and put it into the evidence bag. Then, slowly, they began to stand up.

"We better play this for Sara," said Nick.

After a morning of searching through files and unlocking locked cabinets, Sara and Grissom had uncovered only a few minutes of surveillance footage of the vic. All other evidence that Smith had ever existed had been cleared away. Sara was about to give up any hope that they'd find anything on Smith, when Grissom spotted the locked filing cabinet. They tried every one of Verity's keys, but none of them worked. Grissom had just managed to pick the lock, when Nick burst into the room.

"You're not going to believe this," said Nick, "but our vic left a message for Sara. Warrick and I are still trying to figure out whether he's just scaring her, or if he's threatening her."

Grissom took the tape from his hands. "We got one too," said Grissom. "In here. We heard a click and found the message on the other side of the tape. What did he say?"

Nick gave a brief summary, but Sara wasn't paying attention. She was looking at the file cabinet with curiosity. Inside, she found a box full of labeled audio cassette tapes, and a small packet of papers. Sara picked up the packet, and realized she'd found Smith's file.

It was not a file, in the traditional way a file should look. It was more a list of information. The only name given for the prisoner was "the Doctor."

"Didn't Verity Cordman mention a doctor before she collapsed?" Sara asked.

Nick looked over her shoulder. "Oh, that's what the prisoners called our vic," he said. "They all called him the Doctor. I think it's what he called himself." Nick gave them a brief account of the fight between the Doctor and Sammy.

Sara was looking over the file. There were eight different pictures attached, only one of which she recognized as the vic. Of the other pictures, six were crossed out. One looked as if it were taken from a security camera. She kept looking through the rest of the information.

"The destroyer of worlds," she read. "The bringer of darkness." She looked up at Nick. "It says here that those are his nicknames. Any of those sound familiar?"

Nick shook his head. "They did try to call him toothpick. But as far as I could tell, they just called him the Doctor. Warrick said one guy made a list of all the people they think he's killed, and when he found out he blew a fuse."

"It wouldn't happen to be this list right here?" Sara asked. She turned to the second sheet of the file she was holding. On it was a list titled, "The Doctor's Body Count." Most of the names were written in large block letters. However, at the bottom, another set of names had been added in the warden's own handwriting. Nick scanned the list.

"Yeah, maybe," he said. He pointed to one of the names. "That one. Gallifrey. According to our prisoner, that was the name that really got him mad."

Sara nodded. She carefully filed the papers she was holding under evidence, ready to go back to the lab. Before she could say anything, Warrick poked his head into the office.

"Grissom?" he said. "Don't know if Nick filled you in yet, but you know how the vic was supposed to be paranoid because he thought someone put something in the water? Well, someone did."

The team all looked at one another, and then followed Warrick down to the basement. The basement was filled with old police equipment—batons, barricades, traffic cones, etc. To one side was a large water tank, and beside that sat an enormous bottle of liquid aspirin.

"I didn't think that they made aspirin in liquid form," said Warrick, "or that they'd make bottles of it that big, but there we are."

Grissom went over to examine it. "It's half empty," he said. "I don't know if it's in the water, but they've obviously been using it on something." He took a sample of water, and handed it to Warrick. "Send this down to trace, see if they can tell us what's in it." He then turned to Sara. "I'm thinking I can guess one allergy that's not written down in that file."

"Aspirin," Sara said. She walked over to the bottle, preparing to dust it for fingerprints, when suddenly, the basement echoed with a loud "click".

This time they didn't pause, but suddenly all jumped up and spoke at once, trying to work out where the sound had originated. It was Grissom who found the antiquated black tape recorder hidden behind the water tank. He didn't bother listening to the first side at all this time, just flipped the tape over and pressed play.

"Hello," said the voice on the other end. It was less cheerful this time, much more pointed and flat. Without the cheerful mask, Sara realized that she could hear a terrible weariness inside the voice. If the others noticed, they didn't mention it.

"I'm the Doctor," continued the recording. "Leaving this message for Sara Sidle of the Las Vegas crime lab. Listen very carefully, Sara, because this is vital. Somewhere in this room, you'll find a blue police box… hold on, America. Sorry. You've probably never even heard of a police box before. Looks like a phone booth, but without the glass. Big blue box. Shouldn't be that hard to miss. Probably right behind you."

Everyone looked behind them, but could find no blue boxes. They looked back at the recording.

"Now, I know last time we talked, you thought I was mad. And you're probably right. I get that a lot. But, well, to put it simply, 'I am but mad north-north-west... When the wind is southerly, I can tell a hawk from a handsaw.' So I want you to listen very carefully to what I'm about to tell you. There is something very, very dangerous inside that blue box, and whoever is keeping me here wants that. And if the box isn't there, then… well, that's bad. That's very bad. Not very, very bad, but still bad. Not that anyone can get into it, but someone might still set off the defenses. And that could have some rather nasty side effects. Still, you'll probably find it eventually. Like I said, it's hard to miss.

"Sara Sidle, I know that you're exactly who you say you are. I know that I can trust you. And I'm so, so sorry. I really am. If there were any other way, I swear, I'd do it, but if I really am well and truly dead… I'm going to have to ask you to protect that box. There's a man, about two years from now, Harold Saxon. He's the only person I know who's got the means, ability, and motivation to get into the box and use what's inside as a weapon. If he finds out you have it, he will do anything… and I mean anything… to get that box. Whatever you do, do not give him the box. I cannot stress that enough. He is a master of hypnosis and can be very persuasive, but never, ever, ever give him that box. Don't even let him see it.

"One other thing. If a woman called Sarah Jane Smith comes by and asks to see it, please place this box in her hands. She's a clever one, and one hundred percent trustworthy. Listen to anything and everything she tells you, because I guarantee, you'll need every bit of information to sort out this mess.

"All right, I'm pretty sure that's all I have to say. Be careful, Sara Sidle, and if that police box is gone, be doubly careful. Don't go anywhere alone, keep your eyes and ears open, and if you feel something niggling at the back of your mind, just think nursery rhymes. Good luck, and be brilliant. Message ends."

Grissom stopped the tape, as the others began to search the room. In one corner, Nick found a bunch of old tape recorders covered in dust. It certainly explained where they had come from, though not who had put them there. He was about to point this out to the others, when he heard Warrick's voice coming from the other side of the room.

"Well, it's not a blue phone box," said Warrick. "But it's certainly a phone box sized hole in the piles of junk."

Everyone gathered around and examined where the phone box had been. Sara looked at Grissom, who looked back at her.

"Right," said Grissom. "Gather up all the evidence, we'll meet back at the lab. We've got enough questions; I think it's about time we started getting some answers."