Nancy Drew goes undercover as a transfer student named "Becca Sawyer" at the Waverly Academy for Girls, an exclusive boarding school in upstate New York. The valedictorian candidates have been receiving threatening notes signed by someone called the "Black Cat". As soon as a girl receives two threats, something bad happens to her. One girl had a severe allergic reaction and had to be rushed to the hospital. Another was locked inside a pitch-black closet all night. The parents of the victims are threatening to sue the school if the perpetrator isn't identified quickly. Is there a secret someone wants to protect or are the girls playing games to scare away the competition - permanently? The headmistress is counting on Nancy to solve the mystery before the threats turn deadly.​