In the cookbook school of filmmaking Ruby is strictly leftovers. Begin with a hunk of the occult. Add a cup of 1950s nostalgia, some hardboiled detective, a dash of camp from old horror movies and sprinkle with violence.Most of the pic’s action takes place around Ruby’s Drive-In. Piper Laurie is the one-time gun moll and wife of a big-time mobster. She now owns a drive-in staffed by ‘associates’ of her dead husband. He was gunned down 16 years ago when someone finked on him, but his spirit is back to haunt the drive-in. He gets the job done: a projectionist is strangled with film; a concession stand attendant stuffed into a soda machine; and the dead mobster’s daughter afflicted with a case of the shaking bed. Performances are generally poor.