The college students Doc, Michelle "Mitchy", Mo, Alana, Edward "Ed" and Jackson plot a prank for their college mate Kenny Hampson; however the joke goes wrong and Kenny ends up in a mental institution.
Years later, Doc and Mo decide to celebrate their graduation with a costume party and a magician aboard of a train.
In the embarkation platform, Ed is murdered by a killer that wears his costume of Groucho Marx.
Then he kills Jackson and wears his costume of The Swamp Thing.
The conductor Carne discovers his body, but who might be the masked killer?