Dean and D sat at the table of the girls' hotel room, looking through the Walker file. Samantha sat on her bed and Sam sat on D's bed, each of them typing on their laptops.

D took a moment to pause and rub her eyes. Dean looked up at Sam. "There's nothing here," he said, puzzled. "Nothing we don't already know."

"It's the same thing she told us," D confirmed. "She saw her daughter stab her husband in the living room at the same time she was taking a shower upstairs, and then she disappeared."

"And the shrink told her it was emotional trauma and she was blocking some of it," Dean said.

"And all the rest of that crap," D concluded.

"It's not all crap," Samantha said.

D and Dean both looked up at her like she was crazy. Samantha shrugged. "The mind does work in very strange way. For all we know, Dr. Miller could have been right about her."

Dean gave her a funny look. "So, what, you believe all that psychoanalytic head-screwing?"

A little frustrated, Samantha said, "No, I just think we should consider the possibility."

Now D gave her a funny look. "Why? We never have before."

"I always did," Samantha said.

Dean and D exchanged surprised glances. D shook her head. "Twenty-seven years, you'd think I'd know the girl by now."

Dean nodded sympathetically. "I know the feeling."

"Well, it makes as much sense as this," Samantha said, closing up her computer. "There have never been any violent deaths on Kentucky Avenue, where the Walkers live, since Iola was first founded- at least, not until a week ago, when Mr. Walker was murdered. And the Walker family history is clean- no strange deaths, no skeletons in the closets, nothing. Their about as clean as anyone I've ever seen."

D tapped her pen on the table thoughtfully. "So maybe it's a cursed object."

"I went over everything with the EMF meter," Dean said defensively.

"Nothing?"

Dean shook his head. "Other than the fact that the girl doesn't seem to know how to switch off her stereo, no."

D let out a heavy sigh and looked up at Samantha. "So if it's not the obvious, usual suspects, it could be almost anything."

Dean rubbed at his eyes. This whole thing was getting too damned complicated. "Hey, Sammy," he said, turning sideways in his chair, "how's it going?"

"Not much better, I'm afraid," Sam said.

Dean frowned. "Great."

"There's tons of theories about parallel worlds," Sam said, "none of them any older than H. G. Wells' The Time Machine."

"Why's that?" D asked.

"Well, because parallel world theories focus on the idea that history can be changed," Sam explained. "Until The Time Machine came out, no one ever gave much thought to the structure and mechanics of time. People always assumed that time runs smoothly and cannot be changed. After Wells wrote The Time Machine, some people started to study time, develop some theories, and eventually people came to the conclusion that history can be changed."

D's head was spinning. "Okay, so what does this have to do with parallel worlds and you guys being here?"

"The basic idea," Sam answered, "is that a parallel world is just the way things would work out differently if event in history had hapened differently. if Lincoln hadn't been assassinated, for instance, or if Einstein had refused to build the H-bomb..."

"If dinosaurs hadn't died," Dean said, again referring to Land of the Lost.

"Exactly," Sam said.

"Like, uh... Back to the Future 2," D suggested. "There was a new timeline, and Michael J. Fox had to go back in time to set it right."

"Well, we don't have a time travel problem here," Sam said. "Thank God. It looks like we just jumped timelines."

"How do we jump back?" asked Dean.

Sam scratched his head. "Well, see, that's where the problem comes in. There's more theories about parallel worlds than I can count- but they're just theories. Even a lot of the people who invented them don't believe it's possible to cross the barriers between worlds."

"Oh, it's possible, all right," Dean grumbled. "We got in; now how the hell do we get out?"

"The theories range from the incredible to the impossible," Sam said.

"Give me the incredible first," Dean said.

"Shimmering fog, blinding flashees of light, mysterious waterfalls, severe thunderstorms- all of them completely normal, aside from possibly strange colors, lights, or sounds."

"And the impossible?"

Sam chuckled. "Wll, there's aliens, and time travel, of course. Here's a good one- standing in the center of the Great Pyramid when all the planets of the solar system align."

D grinned mirthlessly. "That's gotta be my favorite."

"Well, there is still one theory that's very disturbing," Sam said.

Dean's eyes widened. "You mean it can get worse?"

"Unfortunately, yeah," Sam said. "There is a theory that the barriers between worlds are invisible and people cross through them every few minutes. These different worlds consist of tiny, insignificant changes, like a germ dies in one world but lives in another. The changes are so insignificant that the barriers between the worlds are completely imperceptible and we pass through hundreds within any given day, replacing ourselves in each world, without ever knowing it."

"Yeah, but this isn't exactly a minor difference," D said. "i mean, on a normal day, men don't turn into women without a complicated operation and a lifetime of hormone therapy."

Dean smirked. Sam gave D a funny look. "Yeah, that's why I think it's probably a visible barrier," he said.

Dean rubbed his forehead in frustration, feeling the beginning of a very bad headache. "Where would it have been? I mean, this is southeast Kansas, man. There's a patch of shifting fog every ten feet."

Sam nodded, frowning. "I know."

"And we went through three thunderstorms between Ohio and here," Dean reminded him. "You telling me it could've been any one of those?"

"Or any one of a number of other things," Sam said forlornly.

Dean rolled his head back and stared at the ceiling. "So to figure out how to go home, we have to figure out how we got here. Which means we have to retrace our steps, so to speak, to find out when it happened and whether anything unusual happened there."

"One thing that'll help narrow it down," D said. "We're from parallel worlds, right? So our lives should be pretty parallel, basically the same, for the most part. Now, if you'd been here for a long time, it's a sure bet we would've run into you a long time ago. So we just have to retrace to where we first deviated from each other's lives and go from there."

Dean nodded, his head spinning. "Yeah, okay, we'll figure it out later. Right now, I think we should keep an eye on that house. After they're asleep, we can run another EMF scan, see if maybe the spookables come out at night." He picked up his duffel bag.

D got up and snatched up her purse. As she turned around, Dean poked a finger in her face. "This time, we take my car."

D rolled her eyes. "Fine, but I still call the shots."

Dean yanked the door open. "Nuh-uh!"

"Uh-huh!" D snapped back, as Dean reached behind him for the doorknob. "My world-"

"My investigation," Dean finished for her. "Yeah, yeah, yeah, I got it." He slammed the door shut behind him.