In the town of Izu known for its hot springs, Den Shichi from Kuromon Town sets off for a healing trip with his companion, a bamboo craftsman with a nose like a lion's snout, at a time when the town is under a tight security network due to a nearby gunpowder depot explosion. Staying at Tsuruya, Den Shichi and his group are investigated by officials whose behavior seems somewhat odd. That night, a man looking like a craftsman is murdered, and gunpowder residue is found at the scene, prompting Den Shichi to suspect that something is amiss.