During a school field trip, Conan and Rachel end up in a mountain cabin with several members of the teaching staff. Conan gets quite a surprise when he answers the doorbell and a frozen teacher's corpse falls into the house! To add to the mystery, a strange letter is written on the teacher's hand, which sends another of the educators running to his room. Shortly after, he's found dead too! Can Conan put his brainpower to work and solve the mystery before the students run out of teachers?