Legacy of a gentle rose cut down in hate

Why did drunken teens kill a young goth?

My Black Rose, her mother called her, in homage to her inky eyeliner, dark dreadlocks and black clothes. Sophie Lancaster was a goth with upwards of 20 piercings in her face, lip and nose and something different down at the core. Or so she liked to think. And yet despite the dog collar round her neck and her pleasure of being singled out in the mosh pit "by a shooting star of saliva from Marilyn Manson's lips" – in the words of the poet Simon Armitage – she was in many ways an old-fashioned soul.

She was happy reading, writing or painting, quietly at home, in the flat she shared with her boyfriend Rob Maltby. The rest of us would probably never have heard of her had the two of them not been, five years ago now, the victims of a brutal attack in a park in Bacup, Lancashire. The pair were kicked and beaten so badly that ambulance staff could not tell which was the man and which the woman when they arrived on the scene.

Yet the strength of Armitage's play Black Roses: The Killing of Sophie Lancaster, which has been showing at the Royal Exchange in Manchester, is that it is about the gentle vitality of her life as much as the savagery of her death. It is the story of a lifetime's love between a mother and her child and how, as she grew, that twinkling child met her soulmate, a man who was as "perfectly weird" as she, "with her banshee make-up and hurricane hair". We get to know her, swiftly but profoundly, through Armitage's deep shafts of poetic insight, and as a result we feel her loss all the more.

"I stand outside this house of justice, not as Sophie's mother, but as her voice," said Sylvia Lancaster when two 15 and 16-year-old boys were convicted of murdering Sophie. Simon Armitage has become a voice of a more transcendent kind. And yet there is a massive emotional vortex at the centre of his poetic drama. It whirls around the question of why a gang of binge-drinking teenage yobs would, without the slightest provocation, inflict such ghastly violence on a pair of kindly innocents.

Armitage gives Sophie thoughts about testosterone and pent-up hate but he – like the rest of us – cannot explain why the studs in her lips, the rings in her ears or something in her vegetarian pacifist lifestyle arouses such a level of fury and depth of anger. The killers do not even know her name and yet detest every atom of who she is: "Something in their lives despises ours. The difference between us is what they can't stand." It was behaviour, a judge said, that "degrades humanity itself".

Sylvia Lancaster, in a desperate attempt to ensure that her daughter has not died in vain, has established an anti-hatred foundation in Sophie's name, turning it to an acronym for Stamp Out Prejudice Hatred and Intolerance Everywhere. Working with police it has entered hundreds of schools with a programme that values difference and nurture tolerance. It has also campaigned for politicians and judges to add subcultural identity to race, religion, sexuality and disability in the categories covered by hate crime laws.

Sophie Lancaster had done nothing more to deserve death than to look different – and intervene to protect her boyfriend, who survived, by wrapping his life in her own. For doing so she was kicked in the head so ferociously that the pattern of her attackers' shoes were imprinted on her cheeks as she lay bleeding from her ears.

"The black roses that bloom on my arms and legs are the bitter bruises of self-defence," Armitage has her say. But there is far more bruised by all this than the body of one single woman. "Call the angels down," she says before the lights fade. "Let me go. Now make this known."