The afternoon before Halloween, Oscar the Grouch receives an invitation to tour an old, haunted castle in Transylvania, once inhabited by Count von Count's long-deceased ancestor, the Grandcount Belugosi, which is said to have been abandoned for 200 years. Sesame Street's resident Grouch must come face-to-face with ghosts who look (and act) eerily similar to the monsters, people and animals he lives with, and must escape the castle before midnight, or else he'll be trapped forever. Along the way, Oscar has to deal with the Grandcount's wicked great-granddaughter, the Countess Ohanna (the runt of the Count's family), who, backed up by Modo and Hugo (two gargoyles who are really bad at being evil), rules the Grandcount's domain with an iron fist. She feigns interest in marrying Oscar by tricking him into believing she is an honorary Grouch (with the intention of killing the Grouch soon after their marriage is finalized).
