A mysterious young girl named Yai transfers into Lan's 5th Grade class. Impressed by her incredible wealth, Lan and Dex unwittingly find themselves trapped on the prococious little girl's estate. All the while, Maddy (an agent for World Three) and her maniacal NetNavi, WackoMan, unleash a devastating computer virus that causes the traffic lights in DenTech City to go haywire, creating an enormous traffic jam throughout the city! Lan jacks his PET into a traffic signal control computer, and discovers that the traffic management center has been infected by a computer virus. Will Lan and MegaMan be able to stop the panic?!