When seventh-grade teacher Mildred Pinkerton is found dead before first period, it's another headache for St. Polycarp's beleaguered principal, Father Felix. Especially when two teachers suspect Mildred was murdered. They've got an empty bottle of pills and a motive: Miss Pinkerton was suspicious of something-or someone-rotten at the school. The victim had requested a meeting to discuss an important matter. Instead, she ended up facedown in her morning coffee. Searching for clues, Julia Hopwood and Amelia Johnston try to connect a series of strange events. The cookie sale money is missing; there's a suspicious new math teacher; and another teacher is hiding a criminal past. When a second death occurs, it's clear a killer plans to teach a lesson in murder that St. Polycarp won't soon forget.