Jonathan Strange & Mr Norrell

9pm, BBC One

I'm not sure if we settled on a name for Poldark fans who were watching less for the stimulating exposition on the Cornish copper mining industry, and more for the bits where Aidan Turner looked in danger of getting his blouse off and giving his hair a damn good tossing. Poldettes? Demelza Poppins? Nampara Teabags?

Whatever they are called, any such bereft souls still mourning the end of the series and searching for a substitute should take care with Jonathan Strange & Mr Norrell. The seven-part drama is set around 1806, a scant 20 years on from Poldark, and the terrain seems familiar. Here you will find men in three-cornered hats, wan women with the fever and, yes, at times, galloping.

However, if this lulls you into thinking that, any minute, you are going to encounter Turner wondering why take two bottles into the shower when he could take only one, be warned. What you are actually going to get is Eddie Marsan, scuttling around in a grey wig, looking anxious and doing spells. And this is not the same thing at all.

A quite lavish adaptation of Susanna Clarke's quite massive book, the series is almost heroically odd. Action unfolds in an alternative-history Britain: the Napoleonic wars are going on, but everything is skewed. Among the more significant differences being that magic is beginning to stir.

We begin in the grey North, with the York Society of Magicians, a muttering club devoted to the history of magic, who prefer to believe it has long died out. Among them, though, a younger member, Segundus (played by Edward Hogg, possibly, on this evidence, the stage name for Robert Peston), wonders why hocus pocus has vanished. His quest for an answer leads to Mr Norrell (Marsan), a reclusive, uptight sort, who turns out to be a practising magician, with a vast arcane library.

After announcing his powers by making the statues of York Minster talk, Norrell and his lowering manservant (Enzo Cilenti) head for London and parliament, planning to offer his services in the fight against Napoleon. But his arrival stirs talk of an old prophecy foretelling the appearance of not one, but two mighty magicians - the other, Jonathan Strange (Bertie Carvel) is a cheerful, slightly foppish sort, with no interest in magic as yet - and the terrible return of the fabled Raven King.

Whether we'll all still be around for that remains to be seen. The series throws itself wholeheartedly into the weird wonders of Clarke's world, and doesn't waste time explaining. But audiences unfamiliar with the book will have work to do adjusting to the stylised climate. We have been conditioned to accept BBC Sunday nights as time for a bit of nice-looking period dressing, whereas Jonathan Strange ... comes on more like one of those grown-up children's shows we get on Saturdays: Harry Poldark And The Order Of The Special Effects Department From Doctor Who.

Given that fantasy has taken over the world, maybe that's not a big problem. More damaging, though, is how, with such a large narrative to get going, the first episode jumps around. A lot happens, but not much seems to mean enough to care about, or leave you desperate to get back into it next week. However, there are enough curiosities to leave you curious. Bertie Carvel's Strange isn't featured enough to come into focus so far, but Marsan's nervy Norrell is an intriguing creation. He might work some magic yet.