Yasako and Fumie ask Yasako's grandmother, Megabaa, to cure Densuke of a deadly illness. In return Yasako agrees to join Megabaa's Detective Agency as their eighth member. Meanwhile, Yūko Amasawa (nicknamed Isako) relentlessly searches for the "Keyhole". Deducing that it resides as an illegal in Densuke, she unleashes her virtual pets to capture him.