Unnaturally close twins Jacki (Judy Geeson, TO SIR WITH LOVE, INSEMINOID) and Julian (Martin Potter, FELLINI SATYRICON, SATAN'S SLAVE) arrive in London to stay in the townhouse of their wealthy father who is staying abroad. When the housekeeper sets out to reign in their childish behavior, Jacki and Julian (with the help of their oracle teddy bear Agamemnon) promptly arrange for the old woman to take a fatal trip down the stairs. The bond between the twins is shaken when small-time criminal Clive (Alexis Kanner) comes into their lives; charming Jacki and alienating Julian (he brings Julian to a motel room to "party" with some transvestites and takes photos for blackmail). When Clive is threatened by a bookie for a 400 quid gambling debt, he shows his true colors but is his brutality any match for the twins' childish (and deadly) games? Based on the novel "Ask Agamemnon" by Jenni Hall, GOODBYE GEMINI (which had its US video release under the title TWINSANITY) is a classy slow-burn treatment of the horror sub-genre about the deadly aspects of the twin bond that thankfully does not degenerate into a PSYCHO-clone (despite the comparisons drawn by the commentators with the Hithcock film as well as WHATEVER HAPPENED TO BABY JANE?). Although Potter has the showier role as the more unstable of the twins, Geeson (a British horror favorite) conveys the underlying menace of her character more subtly (including the funny reply "Don't mind me" when Mike Pratt's bookie apologizes for having to rough up Clive in front of her). Kanner is excellent as the charming Clive who almost seems like the perfect addition to the pair (or trio if you count Agamemnon) until he underestimates them (though a few wiser others have previously remarked that the twins look like they can take care of themselves). Michael Redgrave has a supporting role as a progressive politician who slums in the same circles as Clive and the twins (as well as a snarky artist played by Freddie Jones). Daphne Heard (TO THE MANOR BORN) makes a quick exit as the twins' ill-fated housekeeper. Terry Scully gets some memorable lines as the queeny host of a houseboat party and Peter Jeffrey as a police inspector steals his only scene from Redgrave. Geoffrey Unsworth's cinematography is consistently interesting with layered compositions and wide angle distortions and Christopher Gunning (in his first scoring assignment) provides a fine score. The pop title theme "Tell the World We're Not In" by the Peddlers may seem brash and inappropriate but is thematically relevant given the world the twins have built out together and their attempts to shut others out of it.