This is why I carry a foil of my diabetes medication with me at all times. If Ruthless! were a drink, the imminent British tax on high sugar content would bankrupt this formulation of Marvin Laird and Joel Paley’s 1992 "award-winning all-female-character camp killer cult classic". It’s a formulation which, in narrative terms, partly follows the leaner, meaner version of the show, yet still runs half as long again as the 90 minutes claimed in the theatre’s website.

Perhaps my comments on sugariness are unfair, and it’s more like an alcopop. When the mysterious Sylvia St Croix (who, in this all-female show, is traditionally a drag role) offers to smalltown mum Judy Denmark to train her eight-year-old daughter Tina for her big break, several cans of worms are opened one by one. Young Tina’s savage ambition is unleashed (picture Wednesday Addams dressed as Shirley Temple – on press night, Anya Evans displayed a magnificently annoying helium-Brooklyn voice), the truth about Judy’s parentage revealed, and after relocating to New York City, it all ends with a body count that would instil pride in a Jacobean revenge tragedy.

It’s a show that parodies pushy-mom musicals like Gypsy, an assortment of other sub-genres (Judy gets a number in which she works out on a chair Bob Fosse-style) and any theatrical topic that comes within range: Judy’s adoptive mother (Tracie Bennett, giving a masterclass in acting tipsy but not outright drunk) is a merciless theatre critic who gets a showstopping number entitled “I Hate Musicals”... with two scripted encores, of course.

The thing is that, although neither the content nor the staging are arcane, it nevertheless feels like a piece for the enjoyment principally of initiates: it’s homage rather than satire, with the bite of the alco- consistently outdone by the sweetness of the -pop. Not one of the seven characters gains our sympathies more than fleetingly, yet Richard Fitch’s production (led by Kim Maresca as Judy from the 2015 off-Broadway revival) sets out to disarm us at every step. This is, ultimately, an evening for those who already know that they will enjoy themselves here.

Written for the Financial Times.