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A nerdy guy becomes a lady-killer thanks to an ancient potion in this sexploitation comedy from the 1960s. Henry (Forman Shane) is a nebbish with a mother fixation that's ruining his marriage to his wife, Martha. Henry's psychiatrist suggests he needs more experience with women if he's going to learn to satisfy his wife, but Henry isn't sure how to manage this until he obtains a 17th century diary at an auction that includes a formula for an invisibility potion. Henry brews up the mixture, and discovers it works, with a twist -- it takes effect when he sneezes, and he becomes visible again when he sneezes a second time. Once he becomes invisible, Henry begins creeping through the neighborhood, sneaking into the homes of beautiful women and seducing them, though under the cover of darkness they all seem to believe he's a guy named Jack. While Henry's nocturnal exploits boost his confidence, Martha is soon convinced that her hubby is up to something, especially after a party for her girlfriends is overrun by a pack of invisible mice. Martha also unwittingly learns the secret of the very popular Jack. Henry's Night In was written and shot in the manner of an early-'60s nudie comedy, but since it was made in 1969 it features more nudity than most films of its type; for some reason, the picture was released without any credits for the crew or the creative team.