In the musical Chicago, the real power comes out of a gold-framed, black box sitting centre stage. The box contains the band, which pumps out numbers like All That Jazz, Razzle Dazzle, and Hot Honey Rag. John Kander’s music is indeed the beating heart of the show, although there’s a strong storyline too – a story of “murder, greed, and exploitation” we are told near the beginning. Something to do with 21st-century high finance? No, it’s Chicago in the late 1920s.

Velma and Roxie have both been remanded in what the Americans delight in calling a “correctional facility” on murder charges. “Nobody walks out on me,” snaps Roxie by way of explanation, while Velma simply states: “He ran into my knife ten times”. The two ladies exhibit a vibrant dislike for each other, especially when they both require the services of bent lawyer Billy Flynn to get them acquitted. To the number When You’re Good to Mama, enter prison matron Morton (a splendidly robust performance from Wendy Lee Purdy). A $50 backhander will enable matron to lift the phone to Flynn’s office. Extortionate enough, but the real money comes later: his fee is $5,000.

Many guest artists have played Billy Flynn, but perhaps none more celebrated or unusual than Jimmy Osmond, who takes the role in Oxford this week. Although a slight crack in his voice suggests that eight shows a week on tour is a tough assignment, Osmond sails easily through numbers like All I Care About and We Both Reached for the Gun. As in Cinderella, his Northampton panto debut last Christmas, he seems to delight in blending into an ensemble cast, and there is never any attempt to upstage other people.

And that’s the snag – Jimmy Osmond simply radiates niceness, while lawyer Flynn is as crooked as they come. But, of course, this isn’t a real court, as fans of TV’s Law and Order will quickly realise: no judges snarl: “Objection overruled!”, and Flynn can always call in the dancing girls when his defence case begins to look shaky.

Twinnie-Lee Moore and Emma Barton spit at each other most enthusiastically as Velma and Roxie, while being well matched musically. There is a gem of a moment further down the cast: that heartfelt anthem to the downtrodden and overlooked, Mister Cellophane, is most movingly sung by Adam Stafford. Chorus work wasn’t always quite snappy enough on opening night, but Chicago certainly remains an evergreen piece of entertainment.

Chicago continues at the New Theatre, Oxford, until Saturday. Tickets: 0844 847 1585, or online: www.NewTheatreOxford.org.uk