AN - I meant to say this last chapter, i have no medical training (other than CPR). Please excuse any medical inaccuracies, but i have no idea what the hell i am talking about. Came warning with the science in this chapter.

Chapter 10 – Sisters

Jackson went to the lab. Echo did not let him into the brig to treat Miller. Maybe if he could find something that could ensure Clarke's survival, he could get a reprieve for Nathan. In his head, as long as Clarke made it, there was a chance to save Nate. He pulled a few samples of blood, from when they took them to make Nightblood serum. There was a comparison model built in to the lab. That will be perfect he thought. He'll double check to make sure Octavia's blood won't end up harming Clarke in the future.

He quickly went through the samples, and placed them. He read through them. This can't be right? This must be Abbey's sample the thought. He removed the samples, and saw that it was Octavia's. Maybe they were mislabeled. So he pulled Abbey just to make sure. Again he ran the comparison. This makes sense, it's Abbey's sample, of course there is a DNA match thought Jackson. He pulled Abbey's out, and added Octavia's back in.

A few minutes later Raven found him there. "Hey, what are you doing?" asked Raven.

"Staying busy, I can't think about what's going to happen" he turned around and looked to the floor, and said very softly "They are gonna kill him".

"I think the growing consensus was letting him succumb to his injuries, I'm sorry, but he was never going to stop, you heard him, he blames Clarke for all his own suffering, for some inane reason" Raven responded.

"He thinks that Clarke shouldn't have left them in Mount Weather, he's talked about it before, it goes back to Mount Weather…" he said exasperated, nodding his head. "I should have stayed close to Clarke, then none of this would have happened…"

"Clarke killed everyone in that mountain to save us, and our people, what else did he want her to do? She tried everything" Raven wondered. Jackson could only nod, what else indeed.

Jackson kept scrolling over the same data over and over again. Raven came by and looked over his shoulder. "What the hell? This can't be right" said Jackson when he saw the same results as before.

"What are you comparing? DNA sequences? Why?" asked Raven as she read the results Jackson was reviewing. "I am making sure that Octavia doesn't have any antibodies that would be harmful to Clarke, this thing runs a full panel comparison, including DNA, and it's a 50% match, that could only happen if – if - " he stopped himself, it was so ludicrous, he couldn't say it out loud.

Raven finished it for him "if they share a parent". The both looked at each other, not believing what she just said. "Clarke and Octavia are sisters!?" Raven asked softly. This was mind blowing to the pair. Neither could really let that sink in. "We have to double check these results" said Raven.

Jackson responded "This is my second time. I thought I used Abbey's blood the first time, so of course there would be a match, so I tried again, but no, it was Octavia's" there was a long pause, then he added "This is insane".

"What's insane?" Abbey had come in, she too wanted to check that Octavia's blood wouldn't cause issues in the future, and found the pair looking over DNA strands. "Why are you looking at DNA?" she said as she saw the screen behind the pair.

Neither spoke up, instead let Abbey see the results for herself. Both of them got up and let Abbey sit down. Neither knew how to break the news to Abbey, as they were still trying to understand it themselves.

"This is Octavia and Clarke?" Abbey asked the pair in disbelief. Raven could only nod. "Jaha told me she wasn't a match to anyone alive on the ark… Alive... Jake was already dead… when they found Octavia, Jake had already been floated, I guess that was true" Abbey looked as lost as Raven had ever seen her.

Jackson and Raven were shocked, Abbey spun around looked to the pair. "Jake and Aurora were childhood friends, sweethearts really. But then she married Stephen, had Bellamy, a few years later Jake married me. Right before I found out I was pregnant, we had a falling out, we even talked about getting a divorce it was getting so bad, and Stephen Blake had just been killed in an accident. I knew that they became involved, old friends seeking solace in each other, but then I found out I was pregnant. Jake confessed it all to me, what happened between him and Aurora. So we made a pact, right then and there to try to make it work, for our unborn child, for Clarke. He an Aurora never spoke after that, at least to my knowledge, it was easy really, we didn't really run in the same circles anymore"

If not for Clarke's current situation, Raven would have found all of this to be fascinating, this old gossip from the Ark. "Do you think he knew?" she asked Abbey.

"No, Jake was an amazing father, and he always did the right thing, no matter the cost. If he knew he had fathered another child, he would have claimed her, no matter the consequences, no, Aurora never told him, I am sure of that"

"Jaha knew?" asked Jackson. "The first thing I did when we found Octavia was draw blood, and sent it for a DNA test. I asked someone else to do it though, I could not bear to find out if she was Jake's, I had just lost him. Jaha already knew the whole story, so he said he would confirm"

Abbey turned back to the screen and looked over the other results, after a few minutes she said. "Looks like their antibodies are compatible, not a problem there."

After saying this, Abbey got up, and left the room, she needed to get back to her daughter, knowing if there were complications, it wouldn't come from blood incompatibility.

As she entered the med bay, she spied on Octavia. She was looking for Jake in the young woman. She was all Aurora though, but the eyes, that was Jake's, she could tell that. How had she never noticed that? Abbeyasked herself.

Octavia noticed Abbeys stating at her intently "Was there something wrong with my blood?" she asked.

Madi was sitting near the foot of the bed, by Clarke's feet. Echo and Bellamy were sitting near Octavia.

"No" replied Abbey. She turned to the monitor, and checked her daughter's stats. "Your blood is fine" said Abbey in a small voice. Should she tell Octavia what she found out? She does have a right to know. Will she even care? Abbey was torn. On the one hand, there was still some animosity between them. Eat or die had been Abbey's idea, but it consumed them both. On the other, she owed it to Octavia after everything to be honest with her.

"Something is wrong" said Octavia. By this point she knew Abbey too well to ignore it.

"I don't know if it's my place to say anything" said Abbey. Octavia responded "You said you were going to check my blood, to make sure that it's not incompatible or something, but since I was the only one that matched, what were you checking for? And if you of all people can't tell me something, who the hell can?"

"I –" said Abbey. She was interrupted by the arrival of Jackson and Raven. Raven immediately took a chair near Bellamy and Echo. Jackson went to Abbey and said "The serum is ready for Octavia, I brought it"

"We should administer it then, make her a nightblood as soon as possible. It may go faster with less blood in her system" responded Abbey as quickly as possible hoping that Octavia would now drop the subject. But now it was Raven who couldn't stop staring at Octavia.

"What the hell did you guys find out, cause this is starting to get creepy" said Bellamy as he noticed Raven staring at Octavia.

"Maybe I should go?" asked Raven. She wanted to share the news with Octavia, but didn't want to do it in front of everyone. As Jackson came over to administer the serum, Echo added "Seriously, what could you possibly find in blood to make you look so uncomfortable?"

Raven looked to Abbey, so then Abbey said "We got confirmation on an old Ark rumor, that's all, we shouldn't discuss it."

This peaked Bellamy's interest "What ark rumor?"

"I think if it concerns me, you should tell me, at this point don't we at least owe each other the truth, is saving your daughter is not enough to grant me that favor?" asked Octavia.

"You're right" Abbey said, "Do you want to know first, or tell everyone at once?"

Abbey came over to where most people were sitting.

"Just say it, the suspense is killing me" said Octavia.

Raven looked at Clarke, and Jackson said "I really don't see it" while looking over at Octavia.

"I never met him" said Raven, "Only ever saw a picture" said Raven

"'Him'? What does a 'him' have to do with me, and my blood?" asked Octavia

"You confirmed this rumor? Just now? With blood?" asked Bellamy

Abbey nodded to Raven, she couldn't say it out loud. Raven nodded back, and Abbey moved to where Madi was sitting keeping her vigil over Clarke. Abbey knew that it was going to be Clarke who took the news the hardest.

"They were checking to make sure that Octavia's blood was ok for Clarke, something that should have done before the transfusion, but I guess it was urgent at the time… the things is that the lab is pretty comprehensive, and compared the two samples. The oddity was that the samples shared 50% of their DNA, sooo - "Raven could not finish it.

"50% means?" asked Echo, this was so much beyond her. Bellamy on the other hand was flabbergasted, it couldn't meant what he thought that meant "That's not possible" he said, looking from Raven to Abbey. He saw the truth in Abbey's face, it was true.

Octavia, like Echo had not caught on, "What does 50% mean?" asked Octavia, now worried because of Bellamy's reaction.

"It means that you and Clarke share a parent" finished Abbey. "Jake Griffin, my husband, Clarke's father is also your father" she told Octavia.

Bellamy FLASHBACK:

Five year old Bellamy was making his way back to his bunker. They let them out of school early, so he went into his bunker. His mom was not there. He wanted to surprise his mom, so he hid in the closet. Aurora came in, but she was not alone.

"We can't start anything Jake, Bellamy will be home soon" she told a man, He really could see the man's face, but he could tell he was tall.

"I know, I'm meeting Abbey tonight, we'll sign the papers, and I am a free man, then I can officially meet Bellamy, with nothing hanging over our heads, and it will be like it was always supposed to be"

On a radio the man was carrying, a voice said "Griffin, get you ass to the hab, we need to fix the O2 scrubbers"

"Gotta go" the man said. Bellamy heard kissing sounds, and heard the man leave.

"I remember him, coming into our room; he said something about making it official, it was the last time I ever saw him, he used to bring me toys, even when dad was alive" Bellamy remembered.

"Wait, does that makes Clarke and Octavia are sisters?" asked Madi.

"Yes, Octavia is the only Arker with a bother AND a sister" said Raven.

Octavia just looked at Clarke. They had never been the best of friends, sure they respected each other, but really, they had never been close. In fact, a lot of times Octavia had resented Clarke, TonDC, staying in Polis, the whole bunker debacle. But really, it was about Bellamy. Before the bunker, she knew that other person besides herself that Bellamy loved the most was Clarke, probably still true. It may not be romantic love, but she was sure that Clarke was still part of his "Family". Part of Octavia always resented Clarke for this. But still, at the end of the day Clarke saved the day, one way or another she usually found a way, they were alive weren't they? For this she always respected her, admired her even. To find out that they shared a parent was mind blowing.

"He cheated on you?" asked Octavia, still trying to wrap her mind around it.

"No, we were getting a divorce" Even Madi turned her head when she heard this. "Then I found out I was pregnant. Jake was a good man." Abbey moved towards Octavia, it was important that she understand the next part. "I know, with almost absolute certainty that he never even suspected you existed. Jake was honest to a fault, he always did what he thought was the right thing. It cost him his life. If he'd known about you, he would have come forward, claimed you as his own, damn the consequences"

Octavia just nodded her head. She wasn't sure how this changed things, what this meant to her. She didn't know if it changed anything at all. I guess the only silver lining in all this was she was glad she wasn't successful in he own attempt on Clarke's life.

"I have a sister" said Octavia.

AN - so i know that i have gone full AU here, i know that there is no chance of this ever happening, but it was a plot bunny that would not go away. And i couldn't think of another way to really bond these two characters together. I'll be traveling a little next week, so my updates may slow down. Please excuse any grammatical error. May we meet again!