Acatha screwed up her eyes in embarrassment before bursting through the doors. The observatory was a bustle of activity, people were rushing around everywhere trying to get information, people sitting at computers were shouting at each other. As she scanned the room, she was looking for the blonde hair that belonged to Cameron James, her younger brother.

"Cam!" she called when she had finally spotted him. She rushed over to him, the man following behind. "What's going on?"

"Acatha?" he asked, surprised. "I thought you were in London. How in the world did you get here?"

"It's a long story," she said to him. "Cameron, I'd like you to meet John Smith. He claims he can help with all this."

Smith held his hand out. "Nice to meet you, Michael's brother."

"Michael?"

"Long story," Acatha said again.

Cameron nodded and turned back to the mysterious man. "What's the molecular mass of Jupiter?" he asked suddenly. Acatha groaned. Cameron was probably the only person on earth that knew the answer to that question.

Unfazed, the man rattled off a number with a lot of zeros in about two seconds, and looked at Cameron for approval.

"You're the Doctor, aren't you?" Cameron asked suddenly. "You're here? That's how Ack got here so quickly?"

"How do you know who I am?" the Doctor asked.

"I'm an astronomy student," Cameron said, turning back to his computer. "I've heard all the legends, all the stories. There are people that say you were the one that bought the earth back to where it was supposed to be after the 'Planets in the Sky' incident. I'm probably the only one that believes all of them. What are you doing here?"

"I need to know what you know about the spaceship over London," the Doctor said shortly. As Cameron launched into an explanation, Acatha, feeling obsolete as they talked about spacey stuff, wandered out of the astronomy building and out into the grounds. She looked in the direction of London and realised that the spaceship was a lot bigger than she had originally thought it to be. She could see it from here, although not in the detail she'd been able to see it when she was standing outside her sister's workplace.

She suddenly felt nostalgia. What had actually only been fifteen minutes ago felt like days. This man, the Doctor, had completely changed her world in that many minutes. He talked of such things that would be complete nonsense coming from any mouth but his, and he was absolutely insane. A buzzing came from her pocket, followed by her ringtone. Sighing, she answered her phone without bothering to check the caller ID.

"Mum?" she asked, forgetting that she'd promised she'd be home for dinner. "What's up?"

"Where are you?" her mother asked angrily. "I called you an hour ago and you said you'd be home in half an hour! What's taking you so long?"

"Mum, have you been watching the news? There's a thing up in the sky, and all the major roads have serious accidents on them. There is absolutely no way I can get home. I'm with Lucy at the police station."

"Really?" her mother asked. "I just spoke to Lucy. She didn't say anything about you being there."

"Maybe it slipped her mind, mother," Acatha said. "She's kind of busy. Listen, I'll talk to you later. I have to go. Bye mum!" She hung up before her mother could say anything.

Slipping her phone back into her pocket, she placed her head in her hands. Then she sat up straight again. She had seen something out of the corner of her eye, following somebody into the hospital down the street. But the thing wasn't human. She was definitely sure of that.

Without thinking, she got up and followed it, sure that it was connected to whatever was happening in London. When she was younger, she had played spy games with her brother. They'd developed their abilities of walking silently, blending into the shadows and eavesdropping. It was how they'd found out that Billy, the next door neighbour, was going to therapy because he liked lighting things on fire. Now, she made sure that she couldn't be heard by this creature, whatever it was, and that if it turned around, she could quickly hide.

She followed it all the way to the intensive care unit. Surprisingly, none of the nurses stopped it from walking straight into one of the wards. Baffled, Acatha followed it, making sure nobody would notice that she wasn't supposed to be there. She'd grabbed a coat from one of the corridors a while back, and she'd put it on so that she didn't look suspicious. She could pretend she was a doctor if anybody asked.

The Doctor, she thought. He would want to see this, of course.

The creature was down the other end of the ward, looking at a patient with watchful eyes. Acatha positioned herself near one of the other patients so that she could appear to be checking his vitals while actually still being able to see what the alien was doing. She pulled out her phone and snapped a picture of the thing as it's hand turned into a massive blade of a strange shape, and it shoved it into the patient's abdomen. Immediately, his heart rate sped up dangerously as he lost blood, his breathing became faster, and blood seeped out onto his sheets. Doctors rushed in and crowded around him.

"One of his wounds has reopened," a doctor shouted. Acatha didn't wait around to see what was going to happen. She knew the man was going to die, and that wasn't really what she wanted to see. Instead, she followed the seemingly invisible creature out of hospital and watched as it ran down the street towards London.

Looking up, Acatha realised that the spaceship had moved closer to Oxford. Alarmed, she looked back down at the alien as it made a sound largely resembling a cackle, and a blue light transported it up into the ship.

She ran as fast as she could back to the astronomy building and interrupted her brother's discussion with the Doctor.

"There's aliens on that ship!" she exclaimed breathlessly. "I saw them."

"What did they look like?" the Doctor asked.

"I really don't want to talk about it..."

"Ack, are you okay?" Cameron asked, passing her a rubbish bin. "In there, please."

"I'm not -" she started, but didn't finish because she had vomited into the bin. "Thanks," she said, ashamed.

"No problem," he said. "What happened?"

She took a deep breath, and somebody handed her a glass of water. She accepted it gratefully and started her explanation. Then she remembered the photo she had taken, and handed it to the Doctor.

"Damn," he said shortly. "Michael, why did you follow it?"

"I don't know," Acatha said. "I just... thought something was dodgy with it."

"What kind of blade is that?" Cameron asked. "It's paddle shaped. It doesn't look like it's from Earth."

"It's not," the Doctor said. "That blade is the arm of the Stiltskin race. They live off the energy that people give off when they die... The energy that people give off when they kill them. The real question is, what the hell is it doing in the hospital?"

"Hang on, didn't you say the Stiltkins were the ones responsible for the killings?"

"Yes, I did," the Doctor nodded. "They're from the Hopscotch Galaxy, miles away. That's why I'm confused as to why they're on Earth. Also, now that the police have gotten on board with this one, the killings are going to become more reckless. That's why this one was in the hospital."

"But, it looked like nobody else could see it. It walked straight into an intensive care ward and nobody looked twice."

The Doctor narrowed his eyes at her. "But you could see it?"

"No, I couldn't, which is how I knew what it was doing."

"That was sarcastic, right?" he asked. "Anyway, it seems as though you James clan are different from the rest of the humans. Michael can see things that nobody else can see, and Cameron is almost as smart as I am, which is a very high compliment, my friend. What about Lucy?"

"Lucy has very good instincts?" Cameron said after a while.

"BREAKING NEWS!" the head of the astronomy department called, alerting everybody to the news story that was on TV.

"We go now to Lucy James, the detective in charge of the killings. Lucy?"

"Thank you, Yvette," Lucy said on the television. "We have just received word that there is a new victim of the serial killer. This victim was a patient in the intensive care unit at Oxford Hospital. It is reported that he was attacked by the killer once before, but survived. He had been under close guard. No word yet on how the killer managed to infiltrate the hospital, but we are working on it."

"Ms James," the broadcaster asked. "Is there any information on the murder weapon?"

"All we know is that the blade is paddle shaped. We don't yet know of anything that would fit this description, but we are working on it."

"Do you have any warnings for the people of London?"

"Stay inside," Lucy said. "If you do have to go outside, go in groups of three or more. Stay away from any suspicious characters, and don't talk to strangers. I'm aware that you probably have more questions, but I do need to get back to work. Thank you."

There was silence in the room as everybody took in what Acatha's twin sister had said. Then, almost surreally, Acatha, Cameron and the Doctor walked outside and looked up into the sky. The spaceship was directly overhead.