Disclaimer: Doctor Who (c) to the BBC.

Sarah Jane Smith led a normal life until she was eighteen, and went to university. That's when she started to feel like she was being watched. At first she put it down to stress from working too hard (she was focusing on Extra Terrestrial languages for her current project) and continued to ignore any suspicions, until one day she was approached in the hallway on her way to a lecture. The man told her he worked for an organisation called Torchwood, a secret branch of the government, and they were interested in the work she had been doing. They offered her a job, her dream job, and she accepted at once.

It was difficult explaining to her family and friends why she had suddenly decided to leave university. Torchwood was kept top secret for security reasons, so she couldn't tell anyone that she was still doing what she loved. The only differences were that most of her theories turned out to be true, and she was being paid a ridiculous amount of money to do the thing she had always dreamed of.

When she was twenty-one, a young man called Tobias Reede joined Research and Development. They got married a year later, and Sarah Jane Smith became Sarah Jane Reede. She couldn't have been happier with her life, or her job

"So why'd you leave Torchwood?" Asked the girl sitting before her – the third thing that had suddenly changed her life. The second had been her sudden decision to leave Torchwood two years after the wedding. Toby had asked her the same thing, and she hadn't exactly lied. She told him she was pregnant, (which was true), and that she would rather stay at home and bring up her son than put them both in danger every day, (which wasn't). She had never told him the real reason, because her boss had sworn her to secrecy. She didn't know why she had to tell her strange new visitor the truth – surely she should already know, if she did work there, as she claimed.

"When I tell you, you have to explain what you're doing here. How you found me." Rose nodded obediently, and Sarah took a deep breath to steady her thumping heart, to slow the secret she had kept for nearly twenty years from blurting out. There were times she had almost let it spill out, but she reminded herself that she wasn't allowed, that they didn't want to risk any leak of information, even to her husband.

"Because I found something. Something real - an alien."

The girl didn't even blink, just waited patiently for the rest of the story. Sarah stared at her. Just who is this girl? She found herself wondering yet again. She showed up out of the blue one day, told her she came from London, and somehow further away than Sarah could imagine as well, then refused to tell her more until she had found out everything about the ex-Communications officer.

"I killed it," she confessed, quickly carrying on before Rose could speak, "Well, that is to say, I told my boss about it. Not Pete Tyler, he didn't take over until much later, after I'd left. This was a man called Grady. I reported the finding to him - a spaceship had crashed in the countryside not far away - and requested permission to be on the team that retrieved it. Now I wish I hadn't. We found the ship, and the alien. It looked like…" She broke off and gave a humourless laugh.

"What?" The girl was gazing at her, completely absorbed in the tale. Rose found herself hoping for an alien she recognised, had met, just for some sort of connection to the Doctor. Then she remembered that Sarah had killed it, and hastily took the wish back. She was in luck.

"Like a human, sort of. Like something with only a vague idea of human anatomy trying to pass itself off as a human. It was a kind of silvery-grey colour, like fish scales, and was only about three feet tall. And it had these huge eyes, and arms almost long enough to reach the ground. The team leader told it to come quietly. Most likely it didn't understand him. It didn't answer, just stared at him, standing beside his absurd-looking wreck of a ship. Then when Davis tried to force it to come with us…" She shuddered, looking disgusted and sick.

"It's OK. You don't have to tell me. I'll just leave." Rose began to stand up, was faintly surprised when Sarah Jane grabbed her wrist.

"No! I have to know who you are. And I've been waiting to tell someone the truth for so long."

Rose sat back down, and Sarah Jane continued.

"It killed Davis, shot electricity or something out of its hand. I expect it thought we were trying to attack it. So the others opened fire. They'd given me a gun and taught me how to use it, but I couldn't –" Rose was alarmed to see tears running down her face. Sarah Jane hadn't seemed the sort to cry when she'd last met her. But that wasn't her, remember? That was someone else, someone who'd had the Doctor teach her about what humans do to aliens.

"I felt so guilty. It was my fault they killed that poor creature. It might have had a wife and kids on another planet. Maybe it got lost and crashed by accident. I expect we'll never know. Or at least, I won't – I turned in my resignation the next morning. I couldn't live with myself if I knew that every alien I found and reported ended up killed, just because it didn't understand what we wanted."

"But it wasn't your f –" Rose began, but Sarah silenced her with a shake of her head. It had always amazed her how she'd been able to do that to people.

"No," She said, "I know it was my fault, and I've had nearly twenty years to deal with it. And now I've told you my story, you have to tell me yours. Who are you?"

"You won't believe me –"

"Yes, I will."

And the conviction in the woman's eyes was so strong that Rose thought she'd believe anything she would tell her. "OK. I'll tell you. But you have to promise not to interrupt or ask questions until I'm done."

"I promise." Sarah Jane replied without hesitation. The hunger for knowledge shining in her eyes was intense and slightly scary.

"Well, it started a year ago. When I first met a man called the Doctor…" Rose began, and then the words poured out. She couldn't have stopped them if she'd wanted to.