With just a few days left before Halloween, everyone at Howard Academy is anticipating the guaranteed sugar high they'll experience from gorging on Harriet Bloom's famous marshmallow puffs. The private school's annual costume party revolves around the headmaster's assistant and her seemingly supernatural batches of gooey goodies. So, it's a shock when Harriet's elderly neighbor is suddenly found dead with the beloved dessert in his hand. Police start questioning whether Harriet modified her top-secret recipe to include a hefty dose of lethal poison. Melanie knows her tenured colleague would never intentionally serve cyanide-laced puffs to a defenseless old man. But as explosive neighborhood gossip reveals a potential culprit, it also brings her closer to sealing her own doom.