Kurt & Sid, Trafalgar 2 Studios, Whitehall

The death of Nirvana frontman Kurt Cobain in 1994 has provided a densely populated field of daydreams for conspiracy theorists, several of whom hotly insist that the troubled avatar of Grunge was murdered. Conversely, he may be playing in a ZZ Top covers band in Peru with Elvis and Jim Morrison. Whatever, playwright Roy Smiles has pursued a more original angle.

Picking up on a rumour that there had been somebody with Cobain on the night of his suicide, Smiles exploits Cobain's well-documented fascination with deceased Sex Pistol Sid Vicious, and wonders aloud what would have happened if the spirit of Sid had been "summoned from the desperate mind of Kurt Cobain to debate self-destruction and the pointlessness of suicide".

It's a fragile, fanciful construction, but Danny Dyer (Sid) and Shaun Evans (Kurt, obviously) manage to imbue the claustrophobic two-hander with a resonance and pathos which may be more than it deserves. The tiny Trafalgar 2 is transformed into the spare room over Cobain's garage where he was found dead from a shotgun wound. Cobain's mental chaos is reflected in the random assortment of stuff scattered around the floor -  pizza cartons, toy cars, ashtrays, wine boxes, LPs by The Clash and the Dead Kennedys, a collection of dismembered dolls - while Evans cossets and cuddles the fateful pump action shotgun like it's the only true friend he ever had.

The real-life Vicious was a wasted, felonious punk for whom remaining upright was a significant challenge, but Smiles amplifies and embroiders his spike-haired, swastika-daubed persona to convert him into a shrewd junkie-savant. Though cheerfully coarse and foul-mouthed, leaning forwards with mouth agape and swinging his leather-clad limbs like an ape with learning difficulties, Dyer's skilfully-conceived Vicious gradually reveals hidden layers. He goads the nihilistic Cobain with increasing savagery to take another look at his life and his apparently insurmountable problems, in the hope of planting a seedling of hope.

In contrast to Sid's London-geezer oikishness, Cobain seems tedious and solipsistic, lecturing Sid in a humourless monotone about his gruesome family who loved hunting animals and taunting homosexuals. He even had a couple of uncles who shot themselves. "I've been scared since I was three years old," he bleats. "There's evil out there, man."

"More self-pity," Sid retorts caustically. "Where's the violin?" Snatching up Cobain's laboriously penned note to posterity, Vicious treats it to a scathing critique. "The Lord of the Rings isn't as long as your suicide note, Frodo," he taunts.

As Vicious deploys a cunning selection of devices, ranging from a vein of camp humour that might have impressed Kenneth Williams to exhortations in Latin, Cobain is forced to mount a defence of his commitment to self-extinction. Gradually we can appreciate that he has humour, intelligence and self-awareness, but has reached what, for him, is the only acceptable decision. Not even Sid's furious tirade that a man with a wife and child has no right to top himself can pierce his oddly detached composure. Finally, all Vicious can offer is to keep him company to the end, since he knows full well the horror of dying alone. I kept thinking of a line from the Foo Fighters, the group formed by Cobain's former bandmates - "this is the blackout, don't let it go to waste."

• Until 3 October. Book online here

The death of Nirvana frontman Kurt Cobain in 1994 has provided a densely populated field of daydreams for conspiracy theorists, several of whom hotly insist that the troubled avatar of Grunge was murdered. Conversely, he may be playing in a ZZ Top covers band in Peru with Elvis and Jim Morrison. Whatever, playwright Roy Smiles has pursued a more original angle.

Picking up on a rumour that there had been somebody with Cobain on the night of his suicide, Smiles exploits Cobain's well-documented fascination with deceased Sex Pistol Sid Vicious, and wonders aloud what would have happened if the spirit of Sid had been "summoned from the desperate mind of Kurt Cobain to debate self-destruction and the pointlessness of suicide".

It's a fragile, fanciful construction, but Danny Dyer (Sid) and Shaun Evans (Kurt, obviously) manage to imbue the claustrophobic two-hander with a resonance and pathos which may be more than it deserves. The tiny Trafalgar 2 is transformed into the spare room over Cobain's garage where he was found dead from a shotgun wound. Cobain's mental chaos is reflected in the random assortment of stuff scattered around the floor -  pizza cartons, toy cars, ashtrays, wine boxes, LPs by The Clash and the Dead Kennedys, a collection of dismembered dolls - while Evans cossets and cuddles the fateful pump action shotgun like it's the only true friend he ever had.

The real-life Vicious was a wasted, felonious punk for whom remaining upright was a significant challenge, but Smiles amplifies and embroiders his spike-haired, swastika-daubed persona to convert him into a shrewd junkie-savant. Though cheerfully coarse and foul-mouthed, leaning forwards with mouth agape and swinging his leather-clad limbs like an ape with learning difficulties, Dyer's skilfully-conceived Vicious gradually reveals hidden layers. He goads the nihilistic Cobain with increasing savagery to take another look at his life and his apparently insurmountable problems, in the hope of planting a seedling of hope.

In contrast to Sid's London-geezer oikishness, Cobain seems tedious and solipsistic, lecturing Sid in a humourless monotone about his gruesome family who loved hunting animals and taunting homosexuals. He even had a couple of uncles who shot themselves. "I've been scared since I was three years old," he bleats. "There's evil out there, man."

"More self-pity," Sid retorts caustically. "Where's the violin?" Snatching up Cobain's laboriously penned note to posterity, Vicious treats it to a scathing critique. "The Lord of the Rings isn't as long as your suicide note, Frodo," he taunts.

As Vicious deploys a cunning selection of devices, ranging from a vein of camp humour that might have impressed Kenneth Williams to exhortations in Latin, Cobain is forced to mount a defence of his commitment to self-extinction. Gradually we can appreciate that he has humour, intelligence and self-awareness, but has reached what, for him, is the only acceptable decision. Not even Sid's furious tirade that a man with a wife and child has no right to top himself can pierce his oddly detached composure. Finally, all Vicious can offer is to keep him company to the end, since he knows full well the horror of dying alone. I kept thinking of a line from the Foo Fighters, the group formed by Cobain's former bandmates - "this is the blackout, don't let it go to waste."

• Until 3 October. Book online here