In the world of warrior cats, your main character, a medicine cat apprentice, has the ability to heal cats with a touch of his/her paw, Starclan sends your main character a message telling them that a clanmate is planning to destroy the clans. It is his/her duty to find out who the cat is and stop them. Once they find out who the cat is the cat tells your main character they know about their power of healing and threatens to expose them to the clans. Your main cat thinks they wouldn't be able to continue their training of being a medicine cat, Your main cat is faced with a choice, kill the other cat or expose them and risk being exposed to the clans, or don't try to stop the other cat and live knowing what the cat is trying to do.
What ever your main cat chooses will be the rest of your plot. also if you want a twist ending you could make it so that at the end of the book if your main cat manages to stop the other cat, they realise the cat they were trying to stop was a figment of their imagination, or that they were the main cats other personality trying to take over them all along
