Wildcard Book by Marie Lu

Wildcard is the sequel to the New York Times bestselling novel Warcross. In Wildcard, Emika Chen has barely survived the Warcross Championships. She is now being hunted by a mysterious organization called Zero and his ruthless crew, the Blackcoats. Emika must team up with her newfound allies, including the enigmatic hacker Zero, to uncover the truth behind Zero's plans and stop him before he can unleash chaos upon the world.