First Night: Dallas, Channel 5, 9pm

‘The fun is just beginning,’ says a revived JR – but he’ll have a job convincing us

Josh Henderson as John Ross Ewing and Linda Gray as Sue Ellen (Warner Bros.)

Twenty-one years is an awful long time to hang from a cliff, so I don't imagine even the most devoted fans will have been watching the Dallas reboot to find out whether JR really did shoot himself, as the closing moments of the original series hinted.

Instead, the first order of business for TNT's extension of one of the most valuable franchises in television history was to build some brand new cliffs – and they began with a classic Texan image of good fortune: an oil derrick spurting black gold over delirious drillers. The good news? There's two billion barrels of light, sweet, crude down that thur hole. The bad? The hole is in Southfork and John Ross Jr hasn't yet told his Uncle Bobby that he has ignored his instructions not to drill in the back garden.

It's a big place, but even so you might have thought Uncle Bobby would have noticed. But Bobby, first seen sitting in a doctor's office with an expression honed by 14 seasons of absorbing terrible news, has other things on his mind. Bobby has "a fairly rare form of cancer", the chief symptom of which is an ostentatious wince and a clutch of the stomach at moments of emotional intensity.

JR, meanwhile, is catatonic with depression in a Dallas nursing home and Sue Ellen has ditched the drink and become a political player. Time and the surgeon's knife have been kind to all three, though it occasionally strikes you as fortunate that the drama has never required a huge expressive variability.

"I cain't even quiver ma lip any more," complained Linda Gray in John Barrowman's Dallas, a curtain-raising documentary on Sunday night. That can be a problem with certain kinds of procedures.

The veterans are really there as walking pieces of memorabilia, on hand to give the replica a sense of authenticity. But it's the younger generation who are going to have to carry most of the plot. The principal combatants here are John Ross, who wants to turn Southfork into an oilfield, and Christopher, Bobby's adopted son, who thinks oil is over and it's time to get into deep-sea methane.

And as if this schism over hydrocarbons wouldn't be enough to power the characters' ongoing enmity, the writers have also contrived a sexual overlap. Because John Ross is now paired up with Christopher's old flame Elena, daughter of Southfork's Mexican housemaid.

Just minutes before he gets married to Rebecca, Christopher discovers that Elena still loves him. She thought he'd dumped her by email. He thought she'd run for the border. Neither bothered to check until now, which is handy as far as steamy melodrama goes.

Life at Southfork doesn't appear to be greatly changed. Any large family gathering, as before, is marked by hissing declarations of mutual loathing in back rooms and shirt-grabbing out by the pool. So convoluted is the treachery, indeed, that one of the central characters, notionally acting to rescue Southfork from despoliation, is going behind the back of the person she's already going behind backs for.

And the series' favourite monster is up and walking once again: after John Ross whispers a tonic of bile, rage and prospective oil profits into his ear, JR's eyelids flicker open and a wintery smile of pleasure breaks across his face. He was only depressed, it seems, because everybody was getting on so well.

"The fun is just beginning," he promised his son at the end. It was a promise to viewers too, but on this evidence not one that's likely to be kept. You can reboot a programme. It's a lot harder to reboot a craze.