The ghost of recently dead Mr. Hiram Stokley (Boris Karloff) finds that he has 24 hours to perform one good deed to get into Heaven. He enlists the help of his long dead girlfriend, Cecily, to stop his lawyer, Reginald Ripper (Basil Rathbone), and a henchman from claiming the estate for themselves. The real heirs, Chuck, Lili, Hiram's cousin Myrtle, and her son bring their beach party friends to the mansion for a pool party while Reginald Ripper also employs his daughter Sinistra, and J. Sinister Hulk's slow-witted associates Chicken Feather and Yolanda to help them terrorize the teens, while dopey biker Eric Von Zipper and his Malibu Rat Pack bikers also get involved in pursuing Yolanda for a share of the Stokley estate.
The Ghost in the Invisible Bikini is the seventh (and last) of the American International Pictures (AIP) beach party films and was released in 1966. The entire film takes place in and around a haunted house with no beach in sight, with the teenage gang instead cavorting in and around it and the adjacent swimming pool. Besides the usual bikini-clad cast, random singing, silly plot line, musical guests, and ridiculous chases and fight scenes, the continuity linking this to the other beach films is the Rat Pack motorcycle gang led by Eric Von Zipper (Harvey Lembeck), as well as the appearance of previous beach party alumni Tommy Kirk, Deborah Walley, Bobbi Shaw, Jesse White, Aron Kincaid and Boris Karloff.