Title: Congratulations! It's Twins!
Author: Drey'auc475
Rating: T for content and language
Spoilers: Season 7 of SG-1 and seasons 1-5 of Atlantis
Genre: General/Friendship/Angst/Missing Scene
Setting/Season: Atlantis from its discovery.
Summary: What could have happened if Sheppard had a twin sibling who also had the Ancient gene, and also went to Atlantis with Dr. Weir's expedition?
A/N: I wrote this story to get a little into Sheppard's back story as well as add a new character for the team to interact with. Though she is Sheppard's twin sister, she is still quite different to John in many ways. Most of the stories/chapters will be episode tags and missing scenes. Enjoy.
Disclaimer: Yeah, I don't own SGA (though I'd love to be a part of it) and all of the characters belong to MGM. Except Sierra, of course – she's mine.

-----Chapter 1 – Fragile Balance------
Captain Sierra Sheppard sat in the SGC commissary, eating a not-so-fresh-made turkey sandwich. She had just come back from a briefing on a new fighter-plane that had been developed by the Air Force, using alien technology. She had no idea what she was getting into when her boss handed her the reassignment papers. From the look on his face though, and the way he locked the door when she entered, had originally made her think of something to secret. Though, flying alien-based fighter planes was definitely not the first thing that came to mind.

The first two days of her reassignment had involved signing a non-disclosure agreement, sitting with General Hammond, the CO of the SGC, and watching tapes and footage of offworld missions, getting the low-down from Colonel Reynolds about what to expect on a mission and what and who the bad guys were. They had also told her, and twenty other mid-ranking commissioners like herself, a little about the Stargate though they weren't permitted to go through it yet. But that was ok; she was still getting used to the fact that they weren't as alone in the universe as they had all assumed they were and she wasn't sure that she was entirely ready for that milestone yet.

In front of Sierra currently was the mission briefing that she had received from Major Carter earlier that day. Admittedly, it did say that Colonel O'Neill was the one who had flown the X-302 test missions and the mission that involved them using the hyper-drive to bypass the shields on a Goa'uld mothership. Sierra wondered if she had pronounced that right.

Anyway, Major Carter had taken that briefing to begin with, but later there had been a disturbance outside the briefing room, and a fifteen-year-old kid was permitted into the room claiming to be Colonel O'Neill. The pilots, including Sierra, had thought it was a joke, but when they realized that it really was the colonel, they had all paid a lot more attention. It was quite a shock to Sierra who was still getting used to the place; especially when the control room technician kept calling out "Unscheduled Offworld Activation" over the PA system. It always made her jump when those klaxons went off. She was almost always expecting some funky, tentacle-covered alien to burst out of the air-ducts.

The X-302 was indeed an impressive ship, even though the hyper-drive part of the equation had been removed due to continual failure in the power source. Even though Sierra wasn't a scientist or an astrophysicist, she had spent enough time with Professor Monroe at the Academy to understand that the power requirements for creating that kind of a phenomenon were enormous.

Sierra was skimming through the specs of the X-302 and noticed the G-forces it exceeded and briefly wondered how she could improve her odds in achieving maximum velocity. She glanced about her briefly, making sure that the commissary was fairly deserted, and pulled out a pen and began to scribble on her napkin. A few quick mathematic equations later, and Sierra had her answer. She didn't have much time to contemplate it though, because she was interrupted by one of the scientists sitting down across from her.

Sierra quickly shoved the napkin under her mission briefing and tucked her pen in her top pocket. She glanced up to see that it was one of the astrophysicists that had joined her. Dr. Lee, she thought his name was.

This small, slightly chunky, though genuinely kind, man tried to engage her in conversation. But there were currently quite a few things on her mind, so it was hard for her to get into the swing of it. She was normally quite a talkative person, but she was distracted. She waited for a polite period of time, before gathering her things and bidding the scientist good afternoon.

Sierra was about two feet outside the door to the commissary when she heard it clatter behind her. A second later, there was a firm hand on her elbow and the short scientist shouldered his way up beside her. Sierra stopped and blinked at him, wondering what could have possibly sent him barreling out here like this. She then saw that he clutched the scribbled-on napkin in his hand. She must have dropped it without realizing.

Oh great, she thought to herself.

"Did you do this?" the scientist demanded, causing an irrational flush of irritation in Sierra.

"What, is it against regs to write on napkins, now?" she said, quite rudely. She immediately regretted her harsh words, because she knew that this man was quite nice.

"What? Oh, no," he started, hardly fazed. "I was just wondering... this bit of writing here..." The man was pointing to Sierra's messy scribble. "Is this your work?"

Ah man, Sierra thought and winced inwardly. Having someone recognize her mathematical skills here, was the last thing she wanted. All she wanted to do was to fly X-302s, not sit endlessly for hours staring at equations that she could have done when she was 12-years-old.

"Depends," she said. "How important is it that I say 'yes'?"

"Well," the scientist said as he examined the writing again. "The algorithms are a bit unorthodox, and I've never seen this symbol before..."

"That's one of my own invention," Sierra said. "It's shorthand for e=mc2. I used to teach Advanced Math at the Air Force Academy until recently."

Why did I just tell him that? Sierra shouted inside her head. Inwardly, she cringed again. She was getting slack.

"Really?" the man questioned. "Well, I'm Doctor Lee – Bill. And you are…?"

"Captain Sierra Sheppard, pilot," she said, annunciating the last word, as she took his outstretched hand. He winced and withdrew his hand. She did tend to have quite a strong handshake. It came from growing up with two brothers.

She smiled apologetically at him and he waved it off. Sierra soon realized that he was all business.

"There's something I'd like you to see," he said motioning for her to follow. He led her along the hall and into the lift. He inserted his security pass and punched the button for the fourteenth floor. Soon the lift arrived and they stepped out into a hall that was identical to the one they just left. Sierra had only been in the SGC for three days and was still getting used to the place, and knew that if it wasn't for the three-foot numbers on the elevator doors, then she would have been completely lost. Each floor looked exactly the same.

Dr. Lee led her down the hall, which wound its way around the place, past rooms and labs. They soon came across an open lab door, into which Dr. Lee stuck his head.

He spoke a few words with the occupant of the lab and a few seconds later, Major Carter emerged. Sierra was startled by the major's sudden appearance and snapped to attention.

"Oh, at ease, captain," the other woman said gently. Dr. Lee handed Carter the napkin that Sierra had been writing on and Sierra struggled not to groan. She did love doing Math problems and even teaching it, but to have her work recognized like this? In Sierra's experience, all it caused was trouble.

The major glanced at the napkin as Dr. Lee told her what Sierra had told him. Carter nodded and seemed impressed.

"I was thinking," Dr. Lee said quietly, "that maybe… you know, she could help us out."

Oh, it starts, Sierra thought. Next thing I know, I'll be getting my own lab and research grants –

"Sounds alright to me, Bill," Carter said, and Sierra cringed inwardly. "How are you with velocity and speed?" the older woman asked.

Sierra blinked, slightly startled. "It's my favourite, ma'am," she replied. She laughed lightly. "That's kinda why I became a pilot." Carter nodded understandingly.

"This way." The major led their small group further down the hall and used her access card to open another one of the labs. Inside stood several whiteboards covered in scribbled equations and two blackboards. Computer panels lined the walls, covered in flashing lights. In the center of the room was a steel-topped table scattered with laptops, notebooks, pens and coffee cups. The major and the doctor motioned to the boards.

Sierra was immediately intrigued and wandered over to them, scanning the data quickly.

"This is propulsion," she stated.

"Yes," Major Carter said. "We've been trying to optimize the propulsion capacity of the X-303 – the Prometheus. Using this series of calculations, we've been trying to reprogram the sub-light engines to reach their maximum potential, but our equations have been coming up short." Sierra nodded.

"And judging from your work here," Dr. Lee said, pointing to the napkin that he had passed to Carter in the hall, "I think you might know where we're getting it wrong."

Sierra nodded again, her eyes glued to the board before her. She came across a section of the equation that was unfamiliar to her.

"What's this, ma'am?" Sierra asked.

The major stepped closer to the board. "Oh, that's a part of an equation that Colonel O'Neill wrote some time ago." Sierra raised an eyebrow at her. She didn't know the colonel very well, but Sierra was sure that he was not a mathematical genius. That was her twin brother.

"Colonel O'Neill had all the knowledge of the incredibly advanced race that built the Stargates downloaded into his brain at the time," the major explained at Sierra's look. "Here, this is it."

On the blackboard that Carter was pointing to, Sierra saw that it was covered in an untidy scrawl forming mathematical equations that were indeed complex. A piece of paper had also been tacked to the top of the board with '10=8' printed on it.

Sierra glanced at the equation, the numbers falling out into formation in her mind's eye, like cadets in roll-call. As she looked at the board, the equation spilled into order, forming the solution. "This is base 8 math," Sierra said. "For determining the position of objects in space due to stellar drift."

"Yep," Dr. Lee and Carter said at the same time. Dr. Lee looked astounded and Major Carter looked impressed. Sierra smiled sheepishly at them.

"I studied a bit of your work at the Academy… as a past-time." She said to the major. At the USAFA, Major Samantha Carter was a legend in the area of astrophysics. "Monroe talks about you all the time." Carter laughed lightly and Sierra turned back to the other boards. With this new information now in mind, Sierra was able to work through the equation on the board. Once again the numbers formed into solutions in her mind.


Sierra stepped back into the briefing room on Level 19, and took her previous seat. She had spent the last hour and a half in that lab with Major Carter and Dr Lee, talking over algorithms and mathematics. They would probably still be there if Sierra hadn't glanced at her watch and noticed what time it was.

Luckily, she wasn't the only one who was running late. Many of the other pilots were there, as was the younger, diminutive version of Colonel O'Neill, engaged in conversation with the highest ranking officer in the room, Major Mitchell. When the rest of the pilots had arrived, O'Neill stood at the podium.

"OK," he started, his voice squeaking slightly. He coughed into his hand and lifted a sheet of paper in front of him. "Right, so... As y'all know, you kids are to be the first batch of pilots to fly the X-302s." It seemed a bit strange for Sierra to hear the colonel call them all 'kids' when he looked barely legal himself.

"Now, I'm gonna read out the list of pilots and co-pilots. These pairs are fixed, chosen by myself and General Hammond, and paired this way as a combination of the individual's skills and talents." He coughed into his hand again.

"Pierce and Gander," he started as the names of the first pair of pilots. Sierra's heart pace quickened slightly, excitement flooding her system. She was going to fly again!

"Patterson and Bree; Redmond and Vince; Tander and Banks; Stevenson and Connor; Mitchell and Sheppard; Moffit and Warner, Ash and Jones, Green and Linderman, Gibbs and Wills. OK? Great."

Sierra smiled. She was co-piloting with the highest ranking officer in the new squadron. Major Cameron Mitchell was a very skilled pilot and a fine officer. Mitchell was a legend amongst the younger cadets at the Academy, his piloting and leadership skills earning him a high standing amongst the high-ranking officers at the Academy. Also, her old roommate and best friend, Bryce Ferguson, had served with him. Bryce had also risked his life to save him a few years ago. Sierra had actually bumped into the major as he came out of Bryce's hospital room after the incident that put him in the hospital. Sierra wondered if he would recognize her.

All in all, it was exciting the prospect of being in the air again. Sure, she had once piloted her own plane in the Gulf War with her brother as their squadron leader, but that had been a long time ago. And now she was getting up there again. It didn't really matter to her that she wasn't going to get her own plane, but then again she was only a captain.

And the fact that she was flying with a well decorated officer like Cameron Mitchell… well, it was all much more than she had been led to believe.

Still, thoughts that had plagued her since the short drive from Denver to Colorado Springs now came to the foreground again. Her brother, John, was at the top of the list; in all right and fairness, he should be the one in her seat right now. He was the one that wanted so badly to fly. He was the skilled pilot and she was just the school teacher. She had asked why Colonel Kerrigan had picked her for this job when there were so many others better suited. He had told her that this was her best opportunity for advancement. Sierra had argued that she was happier teaching and that she could name a number of other candidates that deserved the posting. Of course at the time, she had no idea that the new posting involved going to other planets.

The first thing she did after handing her class over to one of the other professors was pull out her cell and call her brother. As she expected, she got his answering service, but didn't really want to leave a message. Instead she called her dad. At first they talked about the weather and his bad knee whilst hers began to ache in sympathy. She soon turned the conversation to her new job opportunity. Sierra confessed to him that John deserved the job more than she did but Dad had never gotten over his eldest son's rebellious behavior. He said that she deserved it just as much as he did, if not more. Sierra, never wanting to get on her father's bad side, had agreed verbally with him, but inside, she was thinking differently.

Sierra wondered if John's actions were really to blame for what was happening to his life. If he hadn't disobeyed that order in Afghanistan, would he be sitting beside her now? Would they be close, like they had been in High School and collage?

Sierra was jolted out of her train of thought, when the klaxons began to flash and the standard announcement came over the PA.

"Ah," the colonel said. "Um, dismissed… until tomorrow, 09:00 hours." And with that, the 47-year old colonel trapped in a 15-year-old body dashed out of the room. Sierra sighed, and gathered her things. She wanted to take a shower before she went over her briefing notes. It was then that she looked down at her page and noticed that she hadn't taken many notes at all. She had been off in her own little world for a good deal of the lecture and had no idea what it had been about.

She sighed and rolled her eyes at herself. She did always tend to have a small attention span. It's not that the lecture wasn't interesting, and she was ashamed to admit that the new form of the colonel wasn't pleasing to look at (she did, however, prefer older guys), but ever since she had taken the Blue Phoenix assignment, she'd had a lot on her mind.

Just as she was standing to leave, a hand was shoved in her face, palm out. She glanced at it, and then glanced up at the person who owned it. She immediately straightened when she saw that it belonged to Major Mitchell. She raised her hand to salute him, but he stopped her mid-way.

"Oh, no, please. There's no need. Cameron Mitchell," he said extending his hand again. Sierra shook it cautiously, sure that she was meant to be placing that hand near her temple.

"Captain Sheppard, sir," she said.

"Sierra, right?" the major interrupted.

Sierra hesitated, slightly startled by this officer. Ok, so she had heard that he was a very casual soldier, but this was a little bit of a surprise.

"Look," he said. "If we're gonna be flyin' together, we gotta be able to trust the other. And I think that knowin' the other's first name is a good start." Sierra detected a bit of a southern 'twang' in his accent and was intrigued. There were two main things she liked about a man: the uniform and the accent.

"Are you from Texas, sir?" she asked, always one to speak her mind.

"Nope," he replied. "Kansas. Little town called Auburn"

"Right," she said, nodding.

"Where d'you hail from?" he asked.

"California originally; my mom was a professional singer from LA and my dad's a bit of an entrepreneur. Needless to say we move around a lot."

"I'd love to hear more about that."

Sierra smiled. "Sure."

At that moment one of the officers touched them on their shoulders. It was Major Banks, one of the other co-pilots.

"Hey, some of us are goin' into town tonight for drinks," he said. "You guys wanna join us?"

Sierra and Mitchell shared a look before agreeing. Several of them remained in the room for a little while, chatting, sharing opinions, and swapping stories of their previous assignments.

Eventually Sierra left the other officers and headed to the woman's locker room. She took a shower, and headed up a few levels to her temporary quarters with some time left over to peruse over the report of the X-302. It was bordering on 18:30 hours when she stopped and dressed in her civvies. She met Mitchell, Banks and some of the other officers at the elevator and together they all headed to the surface.