In this movie, Scooby and the gang have seemed to have split up, but due to their presant situations, decide to team up to solve mysteries in Louisiana.
Slight problem: All the monsters are revealed to be "Bad Guys in Masks", which distresses Daphne, as she and Fred, who currently work at a News station, are searching for "Real Monsters".
A Young woman, Lena, overhears this, tells them that the place she works for is haunted, which gets the hopes of the gang up (except for Scooby and Shaggy.) Taking a ferry, the group heads to Moonscar Island, which was named after a legendary pirate. As it turns out, (in a running gag) the place is full of cats, and Scooby, being a dog, has trouble dealing with them.
After some strange going ons, Scooby, Shaggy, and the rest of the gang, discover that the island has lots, and lots, of zombies, which come from all walks of life, and from over a span of approximately three hundred years, including pirates, Confederate soldiers, and tourists. It is revealed that Lena and her employer, along with the ferryman, are the cause of this: they are werecats who must drain souls of their victims every year so that they can live. With the help of the zombies, who the gang realizes are the Good Guys, the gang manages to prevent the werecats from draining the souls of the intended victims, the gang themselves and the gardener Beau. Cheated of their meals, the werecats' life forces expire, and they dry up into dust, which frees the zombies from their curse, and they go to their Rest.
Or, was that what really happened? What if the werecats managed to survive? What if the zombies did not go to their Rest? What if......?