The remark was uttered in passing by Jonathan Creek, the hero of David Renwick's canny thriller series for BBC 1, and it flags up one of the programme's most appealing features. At a time when many series exploit the audience's untroubled gullibility, this is a drama that makes a virtue out of sceptical thought - and without surrendering any of the Gothic frissons that power less respectable entertainments. Jonathan Creek is a conjurer's ideas man - in other words, he devises and constructs illusions for a popular magician. And, with the convenience we have come to love in genre fiction, the cases that come his way through the agency of Maddie Magellan, an unsuccessful private investigator, are all murderous versions of magic tricks. On Saturday night, for example, it was a sealed box disappearance - a Hallowe'en-costumed murderer retreats into a stone- walled garage carrying the unconscious body of a woman. When the police eventually raise the automatic door, only the woman is lying there. The murderer has vanished into thin air.
Maddie's description of this baffling event is the cue for Jonathan Creek (played with a nice, grumpy bite by the comedian Alan Davies) to look unimpressed and ask apparently irrelevant questions in a knowing manner ("But the paint tins ... were empty?"). It is also the cue for the audience to employ their own brains in connecting the disparate clues, helped occasionally by passages of Socratic dialogue between Creek and Maddie, in which he coaxes her through the inferences and conclusions that will lead to a solution - a chain which depends on logic and the solid physicality of the world rather than alien mind-parasites or poltergeist activity. Renwick has confessed that he wants this series to achieve the same success as One Foot In The Grave - a tricky ambition, if only because the supply of grand illusion devices may run out before the audience has climbed to the same alpine altitudes that the sitcom achieved. It deserves to succeed, though, and not just because the script is fresh and the casting nicely judged. I wouldn't want to get too solemn about it; Jonathan Creek is a game at heart - driven by a pleasure in frankly implausible contrivances. But it is at least a game for grown-ups, and they are rarer than they should be these days.
Unfinished Business, which follows hard on Jonathan Creek's heels, seems to have similar ambitions - the post-watershed timing giving it certain liberties as regards sexual innuendo and verbal abuse. Unhelpfully described by the continuity announcer as a "sharp poke at Nineties life and loves" (which is bound to alert you to any bluntness in what follows) it concerns Amy, a disconsolate divorcee whose most recent lover has been carried off by her daughter. Amy is played by Harriet Walter in a performance that offers strange glimpses of Felicity Kendall - both in the occasional little-girl modulations of her voice, and in the displays of jokey, wits- end hysteria. Her ex-husband is played by Henry Goodman, who is currently stealing the show in the West End revival of Chicago but whose vaudeville manner is a little out of place here - his delivery making every exchange sound like the practised call-and-response of a long-running patter act.
The writing itself is a touch strained, too - prone to elaborate, self- conscious puns. "He works out," says Amy, describing her ex-lover to her ex-husband. "Mathematician?" replies Spike. "That isn't remotely funny," she snaps back, and she's right. Easily the funniest character so far is Ruth, an earnest psychotherapist who provides an audience for Amy's self-flagellating confessions of inadequacy. "What is it about you that invites those close to you to inflict such pain?" Ruth said at one point last night, interrupting a skittish monologue from her patient. That line made me burst out laughing with its dark, deflating solemnity, but I have a feeling it wasn't intended to be funny at all.