Goodbye Gemini is a 1970 British psychological horror film directed by Alan Gibson and starring Judy Geeson, Michael Redgrave, and Martin Potter. Based on the novel Ask Agamemnon by Jenni Hall, it concerns a pair of unusually close fraternal twins, Jacki and Julian, discovering Swinging London while home on Spring Break. Their experiences complicate the pair's relationship, which is already strained due to Julian's incestuous fascination with his sister, which he sees as a natural manifestation of what he believes to be the pair's hive-minded nature.

Judith Amanda Geeson is an English film, stage, and television actress. She began her career primarily working on British television series, with a leading role on The Newcomers from 1965 to 1967, before making her major film debut in To Sir, with Love (1967). She starred in a range of films throughout the 1970s, from crime pictures to thriller and horror films, including The Executioner (1970), Fear in the Night (1972), Brannigan (1975) and The Eagle Has Landed (1976). She played heiress Caroline Penvenen from 1975-1977 in the BBC series Poldark, from the Winston Graham novels.