Under this glamour lens even Cardiff, that dowdy old matron, looked sexy - Vogue post-industrial outside, a world of interiors in. This was a city in which the policemen lived in a loft-conversions with their beautiful American wives, the local GPs dressed as if they were on an Esquire fashion shoot and barely a Welsh accent was to be heard. Not the real Cardiff then, but a time- share salesman's brochure - sophisticated and incredible.
A large poster boasting about Cardiff's new waterfront development filled the screen square-on at one point so perhaps the whole thing was an advert of sorts, the location being just a heroic piece of product placement. Certainly the prevailing aesthetic was a commercial one, in which everything is bent towards glamour - rain, for example, is not a mundane inconvenience or even an emotional device (as it was in some scenes in Prime Suspect, say). It's just a means for getting a nice shine on the road.
Still, it was nice to have things to look at while you waited for the plot to gently unravel. It was a variation on the old identical twins riff - one mad and bad, one sweet and sane (both played by Theresa Russell). The sane one didn't last half an hour, being run over by a sinister white Zodiac outside the off-licence (her champagne effervescing rather beautifully in the gutter). The grieving husband (Jonathan Pryce) soon discovers that her other half has plans to replace her, despite being married herself to an alcoholic policeman investigating a particularly nasty murder.
On Thursday night we were led to believe that the murders had been committed by Mr Phipps, a deranged inmate of the local mental asylum who appeared to be free to come and go on his bike pretty much as he pleased. 'Hate drove the car that killed your wife,' he hissed at Pryce, between bouts of clawing at his face. In last night's episode, though, he ended up giving the Zodiac an involuntary underseal inspection and you had to tick him off your Cluedo card.
In the end it was, as you suspected, the surviving twin, tipped into derangement by envy and unfulfilled maternal longing. The fact that you didn't really care one way or the other about how and why she'd done it brought home what a beautiful bubble the whole thing was - iridescent but empty.