Luigi and mario go to visit peach but find it's under attack by boos. Reaching the top luigi finds mario and peach being abducted to ,as well as star coins, open a portal to The Dark Dimension to use it destroy the mushroom world! During the diaster luigi recoved a grand star coin which he took to professor E.Gadd who uses it to take luigi to the Dark Dimension to collect star coins and grand star coins to continue on. Eventually luigi reaches king boo's castle and defeats him in a final showdown saving the world!