Author's Notes:
Thanks to persiflage_1 for beta reading!

Three a.m., and Sarah Jane was woken by a frantic hammering at her front door. She groaned and pulled the pillow over her head in the hope that whoever it was would go away and let her off the hook, but they didn't, and before too long the noise was joined by the sound of Luke's voice.

"Mum! There's someone at the door! Mum!"

"I know," she muttered. Half-climbing, half-falling out of bed, she dragged on her dressing gown and went to answer.

Putting the chain on as a concession to caution, she opened the door. Outside, in the pouring rain, stood a bedraggled woman in an impractically thin summer dress and rather sturdier, though equally soaked, boots. Her sorry state went some way towards dissipating Sarah's irritation at being woken.

"I need your help," said the woman, her voice full of exhausted desperation. "Please: let me in. Something's hunting me." She threw a glance over her shoulder as she said the last words.

Catching her urgency, Sarah opened the door for her.

The woman slammed the door behind her and leaned against it, dripping. "Bricks and mortar will keep it out, for the moment," she said. "Thank you."

"You're welcome," replied Sarah automatically, and then asked: "Who are you?"

"My name's Romana," the woman said. "You're Sarah Jane, aren't you?"

"I am," said Sarah. "How did you know that?"

"I've heard of you," Romana told her, looking around distractedly. "I hear that you're the person to go to if you're on Earth and in trouble."

"Well, that's very... flattering. You're not from Earth?"

"No, I'm not. Hello." This was directed at Luke, who had appeared at the top of the stairs and was peering down muzzily.

"That's my son, Luke," explained Sarah. "Luke, this is Romana."

"Hello," said Luke, somewhat sleep-befuddled.

"Go back to bed," Sarah told him.

"But mum..."

"No arguing, Luke, please."

Luke obeyed and Sarah led Romana into the kitchen. "Stay there," she told her. "I'll get some towels, and some dry clothes."

*

Warmed up a bit, her dress drying on the radiator, Romana seemed more composed. "I don't know what it is," she told Sarah. "I'm getting closer, learning more and more about it, but I don't know its name. I just call it the Shadow." As she was talking, she was also carefully taking apart and drying out a scanning device of some sort - with one of my good tea-towels, Sarah noticed.

"It doesn't think, it just reacts, but it can learn, too," went on Romana. "Getting into places is what it's good at: it knows how to get into my - ship, but a twenty-first century Earth house like this, made of bricks, is new to it."

The windows rattled, and both women jumped. "Just the wind," said Romana. "We have some time yet."

"But it will get in."

Romana nodded. "You're quite safe, though. It's only after me. It'll go right around anyone else; I've seen it do it. But it can only move at night, for some reason. When the sun rises, I'll go back to my ship, get away. It'll take a while to find me, and I can use that time to work on finding a way to fight it."

"Why is it after you?" Sarah asked.

"I don't know," said Romana. "It's a made thing, not a living creature; someone must have deliberately sent it after me. It doesn't have enough intelligence for me to question it and find out who and why, though," she added, her frustration evident in her voice.

"Can I help?"

Romana laughed - not unkindly, but Sarah bristled with irritation anyway.

"I'm sorry," said Romana, "I don't mean to be rude. Thank you for the offer. But it's taken me months to get as far as I have; I'm not sure I have time to catch you up on even the basics."

Sarah was frowning. "You said it goes around people. Has it done that a lot?"

"A few times," answered Romana, surprised by the question. "Why?"

"I was just thinking - why doesn't it go through them? Why doesn't it even try?"

Romana opened her mouth to reply. "I... don't know," she said. "Maybe it doesn't have time?"

"But if it's so worried about speed," Sarah asked, "why is it trying to get through the walls of my house? Why doesn't it just go under the door?"

"I'm not sure it's got the intelligence to think of that," replied Romana. "It senses where I am and just goes straight for me, as directly as it can."

"But it goes around people," Sarah said again.

"Almost as if it can't go through them," Romana said slowly, catching Sarah's idea.

"That's what I thought. Maybe living tissue can stop it?"

"And maybe that means I can trap it."

"Trap it... do you mean in a person? How would that work? What would it do to them?"

"I wouldn't use a person like that," said Romana. "You're right; the risk to them would be too great, anything could happen. But I might be able to synthesise something... I've been going about this all wrong," she said, impatiently.

Sarah raised an eyebrow.

Romana rolled her eyes, but when she spoke her voice was sincere. "I'm sorry I laughed," she said. "Thank you."

"You're welcome," said Sarah again, and stifled a yawn. "Oh, excuse me."

"You should get some sleep," said Romana. "I'll wake you if something unexpected happens."

Sarah nodded, yawning again, and took herself back to bed.

*

Romana left not long after dawn the next morning, saying goodbye to a still-sleepy Sarah before she left.

"Come back and let me know you're ok," Sarah demanded. "Or if you need any more help, with the Shadow, or whoever sent it..."

"I'll know where to come," Romana reassured her. "We'll meet again, I think."

"I'd like that," said Sarah.

"So would I," replied Romana, and then she turned and was gone, with a spring in her step that hadn't been there the night before.

Sarah watched her go, and then went back into the house. Putting the kettle on for a cup of tea, she caught a glimpse of Romana's dress still hanging on the radiator, and realised with a start that the other woman must have gone off wearing her third best skirt and a t-shirt she'd been rather fond of. She laughed ruefully.

"Hurry back, Romana," she thought, and went upstairs to wake Luke.