Hanging from trees by her knees, doing handstands . . . for Beatrice Zinker, upside down works every time. She was definitely upside down when she and her best friend, Lenny, agreed to wear matching ninja suits on the first day of third grade. But when Beatrice shows up at school dressed in black, Lenny arrives with a cool new outfit and a cool new friend. Even worse, she seems to have forgotten all about the top-secret operation they planned! Can Beatrice use her topsy-turvy way of thinking to save the mission, mend their friendship, and flip things sunny-side up?