The Midnight Warriors book 1

Clara, the most popular girl in school, and Damien, an antisocial prankster, have nothing in common except their friendship. They’ve been friends since they were born. But each of them withholds a secret from the other: they’re both secret teenage assassins from the same organization—and sworn enemies in their alter egos. Hiding under a mask your whole life can flip the world upside down, and that’s what happens to Clara when she finds out Damien’s missing. Clara realizes that he is in the hands of General Skylock, her assassin organization’s fiercest enemy.
Clara must either surrender or face her friend’s death.
Follow Damien and Clara from their points of view as they balance their lives as regular middle schoolers with their sworn obligation to save the world.