It starts with the dark Supergirl telling Kara about how her father Zor-El had sent Kara to Earth for the sole purpose of killing Kal-El because Zor-El didn't share the same philosophy with Jor-El that Kal-El should be the heritage of Krypton. She eventually landed on Earth, but found that Kal-El had grown up and that she would need more time and then kill Kal-El when the time was right. Kara believes her evil self is just lying but she explains that if it's a lie, then how could her evil self possibly exist. Kara attacks her evil self believing she's just a copy and a fake, but her evil self fights back and says that the opposite may also be true. She tells Kara she may not even remember her origin while the evil Kara clearly does. However, Kara refuses to give up and fights back. While they're fighting, the Martian manhunter, Flash, Green Lantern, Black Canary, and Hawkman appear, and the evil Supergirl flies to Earth. Hawkman tells Martian Manhunter he should fly after them as he's the fastest, but he assures Hawkman that the situation is under control. Kara flies after the evil Kara and they both crash on Earth in Gotham City where they encounter Batman. Batman and Kara hold off the evil Kara long enough for Superman and Wonder Woman to arrive. However, the evil Kara refuses to surrender and attacks. In the confusion, the evil Supergirl switches her clothes with the real one and everyone isn't sure who to trust. Superman attacks them both as a result, but the evil Kara (in the real Kara's costume) fights back. The evil Supergirl believes she's stronger than Superman and will beat him because everyone has told her she's stronger, but Superman explains that he's had more experience and can stop her anytime he wants. Wonder Woman then ties her lasso around both of the Supergirls and asks which one is the real one. As a result, the two are merged together into one Supergirl. Superman is relieved that it's all over and Supergirl tells them that she may be dangerous and have done bad things but Superman, Batman, and Wonder Woman all chose to be her mentors and will be with her through all the good and the bad. Later, Supergirl is flying and thinks to herself about how the truth is in everyone and although it will be told differently by everyone, it doesn't matter. She knows that there's only one Supergirl, and it's her.