Murcielago manga volume 20 features story and art by Kana Yoshimura.

Kuroko's group goes to a hot spring deep in the mountains, where the entirety of the land is owned by the wealthy Yamatsukami family. But right as the family is going to decide the next heir, the third son is found murdered... To make matters worse, the only road in and out of the area is suddenly destroyed! Cut off from the rest of the world, the family begins to whisper about a mysterious "Ayako." With little to go on, how will Kuroko solve this closed-room case?