For the writerverse crossover challenge

Sheldon knocked on the door.

"Penny?" Knock-knock-knock. "Penny?" Knock-knock-knock. "Penny?" Knock-knock-knock.

A nervous looking red-head opened the door. "Hello? Who are you?" she asked.

"Dr Sheldon Cooper," he answered automatically. "Who are you?"

"Penny," she replied. "Where am I?"

"In Penny's apartment, that is to say, the apartment belonging to a Penny who is not you," Sheldon said pointedly as if her upsetting of his expectations that the "correct" Penny would open the door was a personal slight. "She's blonde. You, madam, are not."

Not-blonde Penny tugged at a lock of her red hair. "No, I'm not blonde. But I am Penny. Or a Penny. So, I'm in an apartment, which is where, exactly? And, um, just be sure, when?"

"We're in Pasadena," Sheldon said, suddenly excited at the possibilities presented to him, "In California, the United States of America, 2010 by the Common Era."

"That's…nice," Penny said. "I suppose. I haven't travelled in time then…the, er, Common Era, you said?"

Sheldon nodded vigorously. "AD, as my mother would say, but science and religion are very different disciplines and as a scientist, the terms BCE and CE, where CE refers to the common era, that is…"

"Sheldon, what are you doing?" Leonard asked, as he exited the apartment he shared with Sheldon. "Oh, hi," he added, noticing the "Other Penny".

"I am attempting to explain to this young woman, who is called Penny, but is not in fact, the usual Penny, the possible benefits and disadvantages of the dating notation CE."

"Yes, but why?" Leonard asked. He smiled apologetically at Penny.

"Because she claims she has not travelled in time but seems confused by the use of the term CE," Sheldon began again.

Leonard held up a restraining hand. "Sheldon, why would you think she had travelled in time?"

Sheldon tipped his head. "I don't. It was the woman herself who brought it up. She wanted to know where and when she was and then said she had not travelled through time. Obviously, because –"

"Okay," Leonard said quickly before Sheldon could begin a lecture about the impossibility of time travel. "I'm sorry, miss –"

"Penny," Sheldon put in. "I did explain that part."

"We're scientists," Leonard said in the hope it might explain the oddness of the situation.

Penny beamed at him. "Oh, maybe you can help me!"

"Hmm," Sheldon sniffed. "That's how it started with the Other Penny."

Leonard sidled forward to put himself between Sheldon and Penny.

"If we can help, we will. Where's Penny? The one who owns the apartment? Is she a friend of yours? And, er, why don't you know where you are?"

She shrugged. "I honestly don't know. I was in a room, and there was a presentation going on, and then….I was somewhere I can't explain…and then I was here. In this apartment. I know it sounds crazy."

"Sounds like lacunar amnesia," Sheldon said helpfully. "Possibly the presentation you were attending was very boring and, your intellect being overwhelmed, your mind wandered. Your body, however, continued to pursue its mundane and usual actions and so you now find yourself here without knowing how you ended up at this location."

Penny shook her head. "This isn't usual for me," she pointed out. "This is not my apartment. I'm not even from Pasadena. Look, a few months ago, Bad Horse used a teleportation device to escape the police when he was cornered. Maybe it's something like that."

Sheldon and Leonard exchanged glances.

"Bad Horse?" Leonard asked.

"Head of the Evil League of Evil," Penny said helpfully.

Sheldon nodded. "She's either deluded," he said, "Or she really is from some other dimension, universe, or reality."

"Deluded?" Penny shrieked. "I am not deluded."

"We'll figure this out," Leonard said soothingly. "Don't worry, Penny."

"Also, I suggest we call her Penny Number Two, or some such notation to reduce the chances of confusing this Penny with the Penny who is usually here," Sheldon said.

"I suggest not," Leonard retorted.

"I wish Captain Hammer were here," Penny said, "Or, maybe not. Maybe if Billy were here…what? Why are you looking at me like that?"

"Captain what?" Sheldon demanded. "Sounds like a superhero and, Penny Number Two, I am an expert on superheroes and I have never heard of him!"

Leonard sighed. This was going to be a long day.

"Hey…eek."

Leonard glanced over to his shoulder where Raj had just climbed the stairs. Raj had both hands clamped over his mouth.

"Is he okay?" Penny asked.

"He has problems talking in the presence of women," Leonard said. Raj ran over and whispered fiercely into Leonard's ear.

"Yes, I suppose so. I didn't get chance to think about it. Sheldon was bothering her about date notation formats when I arrived."

"What did he say?" Sheldon asked.

"That this Penny looks like Felicia Day, from Buffy the Vampire Slayer and Dollhouse," Leonard said.

Sheldon gazed at Penny for a moment and said, "There is some passing resemblance to Felicia Day, yes, but Ms Day is prettier. No offence," he added. A dazed Penny merely nodded. Leonard sighed.

"Also, she is a virtuoso." To Penny he demanded, "Do you play violin, Penny Number Two?"

"Sheldon," Leonard complained.

Penny shook her head, wide-eyed. "No. I – I could try to play if it's important…"

"Raj, go and find Woolawitz. We're going to need an engineer, and lots of supplies. I believe this woman has fallen into our dimension from other world or reality and it is up to us to return her." Sheldon rubbed his hands together, the look of an evil genius in his eyes. "I think we're going to have some fun. Bwah, hah, hah."

Raj whispered in Leonard's ear.

"Yes, I'm scared too," Leonard said.

Meanwhile, Dr Horrible stared at the blonde woman who had appeared in front him and, in the space of ten minutes, managed to criticise his clothes, his domestic habits, his décor, and his personal hygiene.

She was currently in the process of downing her second margarita. It was the only thing that had shut her up. Threats and proclamations that he was Dr Horrible, of the Evil League of Evil, were met with laughter.

"Of course you are, sweetie," she'd said and patted him on the shoulder. "Now, where's the liquor?"

Dr Horrible was fairly certain this was not how things were supposed to go. For starters, she should be afraid of him. No, no, for starters, this woman should not be here. It should be his Penny, with her quirky smile and poor fashion sense and charitable heart, not this…this…valley girl!

"Explain it to me again, Spock," the interloper said, interrupting his thoughts.

"I'm not Spock," Dr Horrible said testily. "I am –"

"Yeah, yeah, Dr whatever. Everyone's got a doctorate except me." She rolled her eyes. "Oh, and Howard. He's just got a Masters…hah, just says the girl who couldn't complete community college." She began to mix another cocktail.

Moist chose that moment to enter and Penny's eyes lit up.

"Howard," she screeched. "I never ever thought I'd be glad to see you!"

Moist took cover behind Dr Horrible. "What's she talking about? Who is she?"

"Remember how I was trying to teleport Penny away from the Freeze Ray/Death Ray just before the tragic accident stole her away from me forever and bring her here to my lab at the present moment?"

"I recall, since it's all you've talked about for two weeks straight."

Dr Horrible pointed dejectedly to the smoking remains of his teleportation device. "I don't know what went wrong. It sort of worked. But I got the wrong Penny."

Moist shook his head. "Dude, Bad Horse must never find out about this. He'd be pissed!"

Penny laughed. "Honey, I grew up around horses. I know exactly how to deal with naughty livestock. Is he gelded? Because if not, that can be arranged."

Dr Horrible exchanged a glance with Moist. "I need my Penny back."

"I don't know. I kind of like this one."

"We're not keeping her!" Dr Horrible wandered over to his computer. He was not looking forward to making this rather embarrassing blog entry.