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In the beginning, a woman with extremely strong martial arts loves the leader of this heroic clan. However, because she's from this "bad" clan that deals in poison, most people in the leader's clan refuse to allow him to marry her. (He kind of likes her.) While she is staying w/ the heroic clan trying to convince them that she is "worthy" to marry the leader, a plot develops. Basically, the 5th brother in the clan is trying to secretly steal a high level kung fu manual from their teacher's room. He has some other people within the clan helping him. The woman finds out that someone is trying to steal the book, and finds evidence that one of the clan members is suspicious because while trying to help others steal the book, his hand has turned blackish as a result of one of the woman's poisons. While the woman is questioning him in front of the other clan members, the 5th brother shoots a dart and kills him. Then all of the other clan members accuse the woman of killing that guy, but she keeps saying why would I use such an underhanded method to kill this guy? I already had my sword at the guy's neck, why would I shoot a dart at him at the same time? (She makes complete sense.) She continues to say that her martial arts could crush all everyone here. There is no reason at all for her to do these things. All of the clan members still accuse her of killing the guy. Finally, she says, I'm not going to leave here. Let's just wait until the leader comes back and see what he has to say. If anyone disagrees, we can fight to the death. Since everyone knows her skills are much better than theirs, they agree.
When the leader comes back, the woman tells him, you have to believe me. This is crazy that I'm being accused of this. (I completely agree.) However, he says, look, this dart looks like something that you'd use, I'm still suspicious. She starts being frustrated and says I can't believe this, my teacher told me never to trust men. I'm starting to see her point. Finally, the leader says, you stay here, and I'll do some more investigation.
During his investigation, the leader brings back two of his other brothers for assistance. The three of them discuss this for a while, with the two brothers saying that this is more complicated than it seems. During this whole time, the 5th brother is eavesdropping, which he does a lot during this time and is never caught. The two brothers then say they'll finish this discussion tomorrow. In their rooms, the two brothers say to each other, our teacher said that 5th brother has issues and it looks like he is suspicious. When the 5th brother hears the two discussing this, he kills both of them in their rooms.
The next morning, when it is discovered that the brothers have been killed, of course, everyone blames that woman. The leader rushes over to where the woman is staying, and says that we are over, there is nothing but bad blood between us now, you killed my brothers because they were about to tell everyone that you are guilty! The woman says you are a complete idiot, I cannot believe that you cannot see that this is an underhanded plot, can't you connect a few dots together?, why are you believing those fools and not me?, no wonder my teacher told me to never trust men, I will never trust a man again! They fight, she has an opportunity to kill him, she doesn't. She lets him go, but he attacks her again, and injures her. She tells him, fine, if you want to kill me, go ahead, and turns around to let him kill her. He looks at her in anger, and then just leaves.
A while later, the leader's remaining brothers (masterminded by the fifth brother) tell the leader that they need to devise a trap for this woman to kill her because her martial arts level is so high. So basically he goes to the woman, and tells her, I was all wrong, after I investigated I found out that you are innocent, I'm really sorry about this. However, I need you to meet w/ my clan members to clear your name, and after you are cleared, we can get married! The woman says, really, seriously, no way! She falls for this hook, line and sinker. When they are talking about this, she says that she really loves him, and her dream is for the both of them to just retire from the jianghu, and live together in some quiet peaceful place. When the leader hears this, he feels bad about trying to lure her into this trap, and instead tells her, you know, why don't you just stay here, and I'll go clear your name to my clan members myself. However, when the leader's brothers find out that he isn't going to lure the woman to the trap, they have someone disguise himself as the leader in a perfect costume, and go back to the woman and convince her to go to the meeting place. Then they drug the leader so that he is asleep when this happens.
When the woman goes to the meeting place in a cave inside some mountain, the brothers trap her inside the mountain, and set the inside of the cave on fire. When the leader wakes up, he finds out what is happening, and rushes to the cave to try to save the woman. When he reaches there, he defeats the brother who is watching over the cave, and then frees the woman. However, by this time, the woman is badly burned including half her face. She keeps telling him, why did you save me, why did you save me, you should have just let me die, she says frantically. He tells her that he didn't think she would go to the meeting place. She then says that she will definitely get her revenge, and then runs away while the leader is beside himself about what just happened.
Fast forwarding, the woman kidnaps the young daughter of one of the brothers of the clan (maybe 4th brother?). She finds that the girl is very skilled at martial arts and trains her to be her disciple. This girl is the Sister Gan, one of the main characters in this story. When Sister Gan grows up, she is extremely skilled, and her teacher then orders her to kill every single member of that heroic clan...
As I said, I was skim watching this series, so apologies if I made some mistakes in the summary here. The ending of the TV series is as NuDaFu stated.