American Justice, Arts Theatre, London

David Schaal as Herb Stevens (Robbie Jack)

Could you bring yourself to forgive the murderer of your child? There are remarkable people who manage to do so – such as Gordon Willis spoke those heart-rending and politically transformative words after the Enniskillen Remembrance Day bombing. Most of us, though, find it easier to put ourselves in the position of Julie Nicholson who, when her daughter died in the terrorist atrocities of July 7 2005, was unable to reconcile her feelings with her role as a priest in Bristol and made the difficult, honourable decision to resign from the ministry.

Suppose you were an ambitious US Congressman known for your opposition to the death penalty. How would you square your gut instincts and your liberal principles in your response to the illiterate white-trash youth convicted for your daughter's murder? That's the twist in American Justice, Richard Vergette's tense, thought-provoking, but mountingly clunky three-hander, presented now in Lisa Forrell's powerfully acted production.

In a Southern state penitentiary, the drama unfolds over three scenes, the first set at the time of Obama's triumph in November 2008, the second on his 2012 re-election, and the third projecting a victory for the Republicans four years from now.

Daniels, the silvery, distinguished Congressman (Peter Tate) has had the killer's sentence commuted to the life imprisonment on the (unlikely) condition that he teaches him to read. It's a project that initially looks doomed because of the aggressive resistance of Ryan Gage's Lee, and the violent hostility of the red-neck prison governor (David Schaal) who hates liberal politicians almost as much as he despises the “retards” in his custody.

But then a discovery about Lee's poor eyesight causes a breakthrough and by 2012 it's all spectacles, smiles and chats about irony in One Flew Over the Cuckoo's Nest – until the President calls offering Daniels the job of Secretary of State for Education.

As Bryony Lavery's superb play Frozen demonstrated, forgiveness can be the subtlest revenge of all, triggering intolerable remorse in the killer. But the point about mixed motives is that we need to see them operating in painful consort. Here, though, the conflicts between the Congressman's agendas (idealism, career, vengeance) are uncovered in a series of thriller-ish twists leading to eleventh-hour revelations and ripostes that may or may not be true.

What could have been a subtly ambiguous debate about revenge, justice and redemption through education ends in the crude symmetries of melodrama.

To 9 February; 0207 836 8463