The group of Kuroko arrives at a hot spring inn deep in the mountains. The surrounding area is owned by the wealthy Yamazukami family. Just as discussions about the inheritance of the family head were about to take place, the third son is discovered brutally murdered, and the situation takes a drastic turn――. With the only road cut off and isolated from the outside world, whispers of the name "Ayako" circulate among the members of the Yamazukami family... How will Kuroko respond to the series of murders occurring in this sealed space? Additionally, as a commemoration of the milestone 20th volume, a luxurious illustration gallery by a stellar lineup of authors is also included!