Lego Ninjago 2: Mask of the Sensei
"Cole, Zane, Jay, and Kai, the Masters of Spinjitzu, have defeated unbelievably powerful foes and all seems well on the world of Ninjago. But all that changes when the ninja are attacked by the one foe they can't possibly hope to defeat, the one who taught them everything they know--Sensei Wu himself! This is a nightmare come true when they must somehow defeat their respected teacher and friend--or do they?!"--P.  of cover.