Josie hasn't seen her mother in 15 years, not since Fay murdered her father in a rage. Now a grown woman, Josie has come to pay Fay an unexpected visit in a Scottish prison, where she remains locked up for life.

Josie has no memories of her parents or, in fact, anything before the age of 11 when, one morning, she woke to discover her father's bloodied corpse. Fay has nothing but memories. Over a series of visits - at first tentative, later moving and explosive - the two women get to know and love one another. Both troubled, they attempt to live vicariously through the other: Fay wanting a present in which she, through her reserved daughter, is able to experience anew romance, spicy food and nights out; Josie craving a past and a childhood brought into sharp, fully explained, focus.

Rona Munro's script, under the direction of Roxana Silbert, develops this unusual mother-daughter relationship beautifully, while weaving in additional strands of both the personal and the political. Inhumanities of incarceration. Legal prejudices. Values placed on human life. Different forms of love. The scorching heat of passion and anger combined. All of these enrich the play and elevate it far above clichéd prison drama.

The production is also enhanced immeasurably by two sterling performances from Louise Ludgate and Sandy McDade as Josie and Fay. Ludgate's neat business attire, designer shoes, slicked-back hair and professional success "in personnel" belie Josie's real insecurities - her isolation and profound unhappiness.

At turns affectionate and then manipulative or spiteful, you can't help but root for McDade's mercurial Fay, even as you question her trustworthiness. Amongst the play's most electrifying moments are those when she's incandescent with joy at the memory of her late husband. You never doubt that she loved him and misses him dearly still, which makes her motivation for murder especially surprising. What's more, the physical transformation McDade achieves following Josie's cellblock hunger strike is nothing short of astounding.

In the supporting roles of the guards who endlessly patrol Anthony MacIlwaine's greyed-out set of clanging walkways and staircases, Ged McKenna injects flashes of wry levity while Helen Lomax acts as an interesting counterpoint and contemporary to Josie, though she lacks the emotional finesse to make the contribution as powerful as it could be.

Still, Iron - originally seen in an award-winning season at the Traverse Theatre during the 2002 Edinburgh Fringe - is as heavy-duty as its name. First-rate new drama.

- Terri Paddock