SERIAL KILLING, one would imagine, is a serious business. And an actor playing a serial killer would have his work cut out preparing for the role. But what about an actor playing an actor playing at serial killing? In a musical? Well, in Douglas J Cohen's 1997 off-Broadway musical No Way to Treat a Lady, Tim Flavin is having a ball. As Kit Gill the role-playing murderer, he gets to sing, dance, laugh maniacally and dress up as a priest, a flamenco dancer and a stiletto-heeled woman. He gets the best tunes in a weak score, and, perversely, he's just about the most credible character in the whole show.

Adapted from William Goldman's thriller, Cohen's musical is set in 1970, and opens with Gill and Morris Brummell (Paul Bown), mother's boy and dishevelled NYC cop, on a split stage. Morris laments the success of his medic brother, frequently mentioned in the New York Times; Kit laments the fact that his only mention in the Times's obituary of his unloving mother, a Broadway legend, is as "unemployed actor". Both of them sing of the need for "a life". But, while Morris gets his packed lunch from his interfering Mom, Kit gets straight down to business, strangling his first victim. When this fails to achieve the necessary notoriety, he is on the phone to Morris, assigned to the case, to demand that his next murder get the attention it deserves.

So two mother-dominated men find their telephone wires entwined. Once these parallels have been established, Morris's detective work amounts to waiting by the phone for Kit's post-mortem updates - and the rest of the plot is as uninspired as the shabby set. Morris meets Sarah (Joanna Riding), a sophisticated art dealer. Inexplicably, she falls for him, gets jealous that he's spending his quality time with the killer, and gets as excited as Mom when Mo finally makes the front page. But when, in the second act, she joins with Mom in a lamentable song about how much his obsession with the killer has changed him, it's the sound of a writer heavy-handedly basting a turkey with some pseudo-psychological depth.

Bown does naive ineptitude well. But further character development is prohibited by the one-dimensional caricatures alongside him. Joan Savage is a show-stopping Jewish matriarch; Riding sings a song about her sophisticated art-dealer lifestyle life entitled "One of the Beautiful People". But the rest of it was good, tacky fun, largely due to Flavin's cute, demonic Kit, and a multiple-personality performance from Donna McKechnie as all his victims and the ghost of his mother.

For a masterclass in multifarious performance, the three members of the Anglo-Swiss company Brouhaha can oblige. The Opium Eaters, "inspired by" Thomas De Quincey's Confessions and Sergio Leone's Once Upon a Time in America, according to the programme, was at the BAC this week prior to an Edinburgh run. Allison Cologna, Jane Guernier and Catherine Marmier step out of what seems to be a wardrobe, wearing grey straggly wigs and tatty overcoats, and dejectedly share an opium pipe to the sound of the Charleston. Soon, the wigs and coats are off and they're flapping and bum-slapping away; the wardrobe opens out and we're transported back in time to Madame Vaugn's house of ill repute. Custom has dried up; the three negligee-clad women have nothing to do but pass the time.

What follows is an immensely entertaining hour of comedy, slapstick and mime, which somehow makes the familiar ridiculous and the ridiculous reassuring. The performers manage, in the midst of the mania, to imbue their respective characters - all three are "Madame Vaugn" - with a distinctive personality, and a touch of pathos. Tautly directed by Paul Hunter, the energetic set-pieces are superb, particularly a slow- motion three-way fight, set to what sounded like a Seventies sports-show theme-tune. It's quite a shame, when the opium-induced dream/memory fades, to see the three disappear back into their Tardis-like wardrobe.

Summer arrived just in time for the New Shakespeare Youth Theatre's ambitious production of The Jungle Book at the Open Air Theatre in Regent's Park. The 35-strong company of 12- to 16-year-olds, including four different Mowglis, presents a dark, violent tale, closer to the original Kipling than to the singalong Disney cartoon. Among the man-pack alone, the body- count reaches double figures, and the action ends with a showdown between the jungle-law-abiding wolves and a rampaging pack of wild dogs.

Apart from a leather-jacketed, slinky Bagheera, an avuncular Baloo in shabby overcoat and trilby, and a fluorescent orange Shere Khan, the animal characters wear peach Indian trouser suits. Their trans-species metamorphoses were signalled by different coloured baseball caps, but attempts at appropriate animal movements were uneven. Ben Read's superbly slithery Kaa and Shaun Ricafranca's shambling Baloo were the exceptions.

The lack of distinction between the other members of Mowgli's jungle family, along with a breathless race through a wordy and involved plot, seemed to stretch the concentration of the toddler-heavy audience sweltering on the terracing. And a musical section featuring alcohol-guzzling and fag-smoking villagers - "Does it make them clever?" the animals asked Mowgli; no, kids, it makes you stupid and smelly - was just a bit too close to the interval for its message to register. By then, the kids in the audience only had ice-cream on their minds.

`No Way to Treat a Lady': Arts Theatre, WC2 (0171 836 3334), to 23 Aug. `Opium Eaters': Edinburgh Theatre Workshop (0131 226 5425), 17-31 Aug. 'Jungle Book': Open Air Theatre, NW1 (0171 486 2431), to 5 Sept.

Robert Butler is away.