There's a town with a popular laundry business. It's run by the monster Brethren, a creature that can clean anything to perfection. The locals are thoroughly happy with its work, and the children love to be around it. But one day, this beloved monster is wrapped up in a case that affects the entire world!

Kuroki, a fellow researcher who worked with Haibara in the past, fell into a pit and find a lid. It seems human emotions like evil and greed are enclosed by the lid. Kuroki is urged by a grotesque monster named Mahler to open the lid.