Fantasm is a hilarious sex comedy that revolves around a neglected wife exploring her sexual fantasies. With an Australian setting, the film features various sexual scenarios including simulated fellatio, underwater sex, strip poker, and more. It delves into the world of swingers, sexually frustrated women, and mature woman/younger man relationships. The film also touches on controversial topics such as rape fantasy and incestuous relationships. With its sketch comedy style, Fantasm offers a bold and explicit exploration of human sexuality.

Libbie is assigned to her paper's sexual advice column, "Dear Collete". She is taking over the job of Harry a crusty old journalist who shows her the pro's and cons of the job while running on a tight deadline to get the column finished for the morning's paper. During the course of the evening they reply to a wide variety of sexual experiences submitted by the readers, some these include, sex in a threesome at a drive-in theatre, sex in a gymnasium, and sex in a library where the "Silence Please" sign gives the male librarian an advantage over the female readers.