D: Alan Gibson. S: Edmund Ward. Novel: “Ask Agamemnon” by Jenni Hall. P: Peter Snell. Cast: Judy Geeson, Martin Potter, Alexis Kanner, Freddie Jones, Mike Pratt, Peter Jeffrey, Michael Redgrave. UK dist (DVD): Odeon Entertainment.

A mildly diverting “Age of Aquarius”-era Psycho-thriller distinguished by a solid Brit cast, trendy direction (by future Dracula AD 1972 hand Alan Gibson) and an unusually sober attitude to the hokier elements of its scenario (thanks, perhaps, to the story’s literary origins: 1964’s “Ask Agamemnon” by Jenni Hall). Horror fans hoping for a lurid exploration of the time-worn good twin/evil twin trope may be disappointed, but Gibson and producer Peter Snell (The Wicker Man) are concerned more with exploring the tragic bond between the siblings than with accumulating a succession of fashionably gory shocks.

Judy Geeson and Martin Potter play twins Jacki and Julian, orphaned teens with a decidedly unhealthy relationship: with little comprehension of the world outside their own hermetic existence, their behaviour is disconcertingly childlike, much given to pre-adolescent play and acts of conscienceless malice – and shot through with intimations of sublimated incest. (We fast infer that Julian is struggling with the urge to de-sublimate, a development of which Jacki seems blissfully unaware.) The third component of this troubling ménage is the teddy bear Agamemnon, silent confidante (and adviser?) to the pair; his glassy stare takes in many a candid moment.

Arriving in London, Jacki and Julian swiftly quash any threat of adult intrusion in their cosy lifestyle: a vicious practical joke disposes of an interfering old landlady, specs ground underfoot and the wearer sent (with Agamemnon’s collusion) on a one-way tumble down the stairs (what larks!). But the grown-up world refuses to keep its distance: part-child, part-adult, brother and sister exert a deadly fascination for the characters who cross their path. At a transvestite strip joint (far out!), they hook up with charismatic party animal Clive (Alexis Kanner): enabler, libertine and blackmailer, with more than a few unpleasant pranks of his own to play. But Clive has badly misjudged his prey; and when the cruellest of his schemes – involving a seedy hotel room and a brace of tranny hookers – finally tips poor Julian over the edge into paranoid psychosis, innocence is only the first victim carted from the arena…

Fresh from Fellini’s Satyricon (and subjected here to more Felliniesque indignities), Martin Potter comes off as strangely flat as the loopier half of the zygote, though he tries hard. Judy Geeson, effortlessly lovely, fares better (though hers is the easier part, of course). Building on his appearances in McGoohan’s The Prisoner, Alexis Kanner continues to position himself as a one-stop-shop for eye-rolling sociopathy and counter-cultural weirdness; here deploying the self-same mid-Atlantic “groovy accent” and adventurous sideburns (though minus the top hat), one assumes his offscreen persona must have required very few tweaks for him to get in-character. The rest of what Kim Newman has cattily (though not inaccurately) described as Goodbye Gemini’s “overachieving supporting cast” includes the ever-reliable Freddie Jones as a fruitily sardonic (=homosexual) art dealer; Peter Jeffrey in a stroll-on, stroll-off role as Baffled Police Inspector, not for the first time and certainly not for the last; an authentically-raddled Mike Pratt (Randall and Hopkirk [Deceased]) as a ruthless debt collector, sporting a coat best described as “decomposing Afghan”; and lastly, and most surprisingly, the legendary Michael Redgrave as a respected TV spokesman for progressive politics, with less-than-grandfatherly designs on young Jacki.

The soundtrack is comprised mainly of chart-friendly flower-power numbers, although Christopher Gunning’s Satie-inflected compositions occasionally aspire to the innocent lyricism of his later score for Hammer’s Hands of the Ripper (another unhappy tale of tarnished youth). As for exploitative elements: surprisingly few and far between, limited to a couple of bare bums and topless demimondaines to remind you what a wild and crazy scene the kids of today inhabit. A stylized bit of mayhem involving a pair of ornamental disembowelling-cutlasses ought to raise a smile, too. Odd but not compellingly so, Goodbye Gemini falls somewhere between the grimy nihilism of Pete Walker and the quirky charm of Hitchcock’s Frenzy (1972). Fans of Swinging-London cinema will already have clocked this as a must-see; the rest must take their chances.