There is nostalgia, and then there is the unclassifiable emotion that is flooding Wembley Arena as 12,000 women await the Osmonds, who have regrouped for the first time since 1980 to celebrate their 50th anniversary. Despite the questionable pretence - they may have formed in 1958, but opportunity did not knock until the 1970s - the show is sold out, and for many fans, it is as if the last 30 years simply never happened. There are tears and volcanic gasps.

A matronly type in an "I Love Donny" T-shirt cannot stop screaming the name of the purportedly cutest member of the group. The emotion is heightened by a video of the group's arrival in London in 1972 when they were mobbed by bawling girls, some of whom are undoubtedly here right now.

The original blow-dried fivesome have been augmented by younger siblings Jimmy and Marie, but only one Osmond has the key to these female hearts. White-bearded Merrill, goateed Jay and the rest diligently do their thing, but they are mere adjuncts to Donny, who has the square-jawed openness of a midwestern congressman. He is not at all sexy, especially not when crooning vanilla ballads such as The Twelfth of Never, but there is no disputing the effect he is having on everyone around me.

The Osmonds were a potent boy band because of their can-do energy, and the odd great song such as Crazy Horses (which opens this show with mad gushes of dry ice and stamping feet). As adults, the attraction is much diminished.

They shuffle through the set by rote: Down By the Lazy River, Let Me In, a medley from the "concept album" The Plan. But the only sibling with a spark of life is Marie, who sassily flirts with the three male members of the audience and makes the set worth watching.

Where are the Jackson 5 when you need them?