When a local operetta production is plagued by ghostly events, Fenton P. Smith and Gerald Grubbs, a.k.a. the Determined Detectives, are thrilled. This could be their best case yet! In this hilarious and spooky whodunit, the boys - and their arch rival Mae Donna Dockstadter - go undercover. Posing as extras in the cast, they set out to investigate the haunted opera house and unmask the Phantom of the Operetta.