A race in Cloudsdale against Rainbow Dash and Cloudkicker goes horribly wrong when Cloudkicker is found dead and Kat is found right next to her body. She has no memory of killing Cloudkicker during the race but does have memory of Cloudkicker attacking her. Eventually Kat learns that she is responsible for the murder of Cloudkicker only it's not…her.
Deep inside of her head there's another pony who's just like her only…different. This pony has a lust for blood and loves to kill. She is not afraid to come out of her cage and unleash herself in front of the world. This other pony is known as Kit, Kat's split, murderous personality.
Now Kat is trying to find a way to control herself as well as Kit from killing any more ponies. But, past experiences is strong in Kit's "heart" and she is out for revenge on every pony who has messed with her. Can Kat control Kit? Or will everything end up in a bloody war?