On the day of the parent-teacher visit at Teitan Elementary School, Conan and the Detective Boys prepare for their parents' arrival. Haibara appears indifferent, while Maria is worried because her mother insists on coming despite her back injury. In front of the school, several children shop at the store: Maria buys tape, Takuma gets a notebook, and the newly transferred student Kaisuke shows interest in potato chips. Kaisuke then spreads a horror story about a "man-eating classroom" that must be appeased with snack offerings—and claims the ghost is now in their school.

During lunch, an unexplained fire breaks out in the flowerbed outside the classroom. Haibara quickly extinguishes it with water from a vase, but the cause remains a mystery. Conan finds burnt potato chip remnants and suspects three people with motives:

- Kaisuke, who might have started the fire to prove his ghost story;
- Takuma, who could be covering up a trampled tulip during the solar eclipse;
- Maria, who may want to cancel the parent-teacher visit to spare her injured mother.

When teacher Kobayashi considers canceling the visit, Conan promises to solve the case in the remaining 10 minutes of recess. His experiment with a broken kitchen timer from the workshop leads to the crucial clue: A 10-yen coin is missing from the battery compartment, and only one of the suspects could have possessed it. Conan reveals that the culprit constructed an automatic ignition mechanism—and identifies the guilty party before the evidence disappears.