On paper, Diamanda Galas's latest performance, brought to the UK as part of the Barbican's Only Connect series, is a simple one-woman show. But in the flesh, the violent versatility of Galas's voice brings a terrifyingly vivid kaleidoscope of peoples, languages and horrors to her 90-minute set.

Part theatre, part cabaret and part supernatural song-cycle, Galas's Defixiones, Will and Testament incorporates wild arrangements of Ornette Coleman and John Lee Hooker alongside settings of poems by Henri Michaux, the Armenian poet Siamanto and texts by Galas herself.

Galas's inspiration for the evening comes from a relatively unknown chapter of east European history: the Turkish attempts in 1915 and 1922 to remove the Greek and Armenian populations living on Turkish soil.

Appropriately for a work dedicated to the "forgotten and erased" victims of this violence, Galas begins in a spirit of savage lament, with a searingly intense solo number. Although not directly a folk melody, the essence of this music lies in Armenian culture. Imbued with a hyper-intense, operatic vibrato, Galas's voice seems to come directly from the grieving of an entire nation.

As the set develops, Galas creates alarming musical juxtapositions. In one number, she starts with a piano accompaniment of almost Mozartian urbanity. But her voice intones a César Vallejo poem with grating desperation. Avant-garde explosions start to puncture the piano part before the texture erupts into a torrent of words and music pitted emphatically against one another.

Galas can do things with her voice that virtually no one else can. She is able to create a lucid terror from screams and screeches, as in her setting of Michaux's Poetry for Power. But Galas's real gift is her ability to sustain a dramatic progression throughout the whole set. Tellingly, the later numbers used contemporary styles and forms, in contrast with the ritualistic austerity of the opening.

It is impossible not to be shaken by the gothic seriousness of Galas's vocal and her theatrical presence. This ferocious performance is a forceful and timely reminder of the blood-stained past that forged the superficial contentment of our present.