Deciding to go bowling after they are rained out for tennis, they are met by Makoto, who engages Sera in a fight after mistaking her for a boy interested in Sonoko. After this is straightened out, we learn that he was attacked by teacher Masahiro Tanba, who was drunk. His coworker Sunami Masaki took him to the car to calm down. Makoto soon leaves to nap in the car, not finding bowling to be his strong suit. After a while, math teacher Michiko Monna becomes worried about Tanba, and in going to check on him, finds him missing. They all check around the local bars, but the missing teacher is found drowned in a portable toilet, and Makoto becomes the prime suspect due to the strength required for such a feat. He also had the opportunity, remaining in the parking lot during the estimated time of death.
Sunami discovered the missing Tanba in the toilet in the parking lot of the bowling center. When Sera and Conan examine the body they're surprised to see the cause of death is drowning.
Conan clears Makoto's name through Sleeping Kogoro, and identifies the colleague of the victim Sunami Masaki as the culprit. Sunami locked the door and used kerosene candles to burn the oxygen out of the porta-potty, causing the water from the rain to fill in and rise, drowning the victim. Sunami's motive was to avenge her best friend's, who was Michiko's younger sister, death. Her best friend's goodbye text wasn't about eloping, but of double suicide by drowning, and Tanpa let her die because he became scared, so Sunami drowned him. Sera's other brother is texting her the answers to the case and asks her questions about Conan, arousing her curiosity of him.
