Rehab: The Musical opens with a boyband star, Kid Pop, getting busted for possession of cocaine. The judge sentences him to a course of treatment at the Glade which he attends with great reluctance. Giving up marching powder is the last thing on his mind. ‘I said no to drugs but they just wouldn’t listen.’ His sharky agent, Malcolm Stone, wants to prolong Kid Pop’s notoriety by sending an undercover ‘addict’ to the Glade to spy on him and leak stories to the press. Stone hires a luscious sex bomb, Lucy, to take on the job, and it’s obvious that Kid Pop will seduce her and their affair will end in redemption for both parties.

Predictable enough, perhaps, but the couple’s journey is a joy to experience. Fabulous costumes and an array of ingenious set designs transform the stage into a series of court rooms, nightclubs, therapy suites and hospital clinics. The cynicism of the opening scenes gives way to sympathy for the Glade’s inmates and their woes. One addict is a cross-dressing overeater who loves to wear lipstick and eye shadow. Another is a pale misfit who can’t stop visiting tanning salons. Annabel Giles does a great turn as an ex-Bond girl struggling to beat the bottle.

Elliot Davis’s adroit, quickfire script can shift instantly from cynical wit to emotional tenderness. The double agent, Lucy, isn’t just a greedy bimbo but a divorced single mum involved in a custody battle for her son. Her previous career as a sex worker has damaged her claim to be a responsible parent, and she uses Malcolm’s job offer to bolster her record as a reliable employee. Gloria Onitiri plays Lucy as a confused, frightened and almost tragic figure struggling to overcome the appalling challenges that life has thrown at her. Malcolm Stone, the swaggering street thug, is a role that comes easily to Keith Allen and he reminds us that the career of the scam artist relies on a natural talent for theatrical improvisation. Allen adds comic burlesque to the mix. This tremendous show will attract serious attention from West End investors.

Age Is A Feeling opens with a parlour game. Haley McGee, the writer-performer, announces that she will recite six stories chosen by the audience from a set of 12. The selection is made and the names of the rejected stories are read out. But this makes everyone in the room want to hear the deselected yarns instead. McGee is a young north American with a gymnast’s figure and the looks of a movie star, and her tales purport to cover the full span of adult life from the early twenties to the farthest extremities of old age. It’s not clear how she acquired all this wisdom and where she derived the confidence to deliver it in such minute detail.

Grammatically, she uses the second person singular, future tense, so her stories feel like army orders. ‘You will do this… you will feel that… you will respond as follows.’ Alarmingly, she delivers her life lessons from a white umpire’s chair fitted with a silver bell which she DINGs regularly to underline her points and to help spectators struggling with drowsiness. Though her advice is aimed at strangers, the material originates from a single source. Herself. The emotional texture is limited and rather soppy. Entirely girly, in fact. Some in the audience may be surprised to learn that they will pine for a pet dog, and will fret about not having babies, and will discover love on the back seat of a bus, and will be haunted by the memory of a prettier schoolyard rival named Nemesis. What if you happen to dislike dogs, babies and bus journeys? And some in the crowd may not have attended an all-girls school in America. Too bad. Strap in. More is coming.

In one of the ‘stories’, which are just chapters from an autobiography, the narrator witnesses a nasty collision between a dog and a speeding bus. It feels like a re-enactment of JFK’s assassination. ‘You will see its brains on the road.’ Later, the audience is given details about ‘your parents’ – or rather McGee’s parents. Dad writes obscure military textbooks. Mum is a laid-back groover who advises her kids to cure their fear of death by dropping acid. McGee’s creed, ‘age is a feeling’, is repeated with many DINGs of the silver bell from the umpire’s throne. And she insists that the ‘feeling’ is always a serene and happy one. At the age of 56 – DING! – we’re told that the desire to seek more from life will fade. No, it won’t. And how do you know? You’re half that age. The show finishes with a revelation – DING! – about the parlour game at the start. The six stories excluded from the show are available in a paperback for £7.50. KERCHING!