People have begun disappearing with only their shoes left behind.
The culprit is AncientSphinxmon. The victims are asked to solve a riddle, and when they can't, they are turned to stone. Their stones are then used to build a pyramid.
While investigating the disappearance of Ruli's friend Kaoru, both Hiro and Kiyoshiro fall victim to AncientSphinxmon!
NOTE: This episode introduces Diarbbitmon, the mega evolution of Lamortmon.