Fred (FREDDIE PRINZE JR.), Daphne (SARAH MICHELLE GELLAR), Velma (LINDA CARDELLINI), Shaggy (MATTHEW LILLARD) and his talking dog, Scooby-Doo (voice of NEIL FANNING), make up Mystery, Inc., a crime-solving quintet that's able to crack most any mystery - supernatural or not -- despite their moderate ineptness.
Yet, their differences - Fred being the conceited one, Daphne usually ending up as the damsel in distress, Velma being the brainy one and Shaggy coming off as something of a goofy but good-natured scaredy cat - eventually cause them to disband, much to Shaggy and Scooby's dismay.
Two years later, the group ends up being reunited on Spooky Island, a macabre amusement park run by
Emile Mondavarious (ROWAN ATKINSON) and frequented by those on spring break. While Shaggy and Scooby are happy to see the others and eager to reunite, Fred, Daphne and Velma want nothing to do with the rest, although they accept Mondavarious' request that they get to the bottom of a mystery regarding the island's guests.
It appears that while they arrive chipper, the students leave in something of a zombie state that makes Mondavarious believe a spell has been cast over the island. Accordingly, the former members of Mystery Inc. - and Shaggy's new friend, Mary Jane (ISLA FISHER) -- set out to get to the bottom of the mystery and eventually reunite, all while dealing with various characters and phenomena.