Star Wars - Rebels - The Secret Academy

the long version

"Zare Leonis has reached the Arkanis Imperial Academy, where his sister, Dhara, was taken by evil agents of the Empire. He must win acceptance into a secret society within the school to gain access to the mysterious Area Null, where he believes Dhara is being held. This secret order is loyal to the Academy's commandant and is part of his terrifying vision for the future of the Empire. In trying to save Dhara, Zare will find his loyalty tested as never before and expost old friends to great peril."--Publisher description.