Prior to the start of the novel, Mrs. Sidman was just another teacher at Camillo Junior High School. However, after Doug Swieteck played a prank on her that dyed her face the color of a mango, she became jumpy and terrified of students and left teaching to work in the school’s main office. After heroically rescuing Mrs. Baker's class from the rats Sycorax and Caliban, she takes over from Mr. Guareschi as principal. As principal, Mrs. Sidman truly comes into herself and her power. Holling notes that she masters the "principal look" quickly, and she's a much more competent principal than Mr. Guareschi ever was.