Justice, Old Red Lion Theatre, London

The play opened at the Old Red Lion last Thursday, when London was on a high security alert. It certainly felt weird to be travelling to a post-Troubles drama on an underground system twitchy with apprehension because of a new, more lethal and less limited form of terrorist threat.

Not that these ironic circumstances draw the sting of a play that - like the work of the award-winning Ulster dramatist Gary Mitchell - scrutinises the internecine divisions within the Protestant community as it struggles to adjust to the implications of the peace process. Here the focus is on the bloody feud between two paramilitary groups: the Ulster Volunteer Force, which has been on cease-fire since 1994, and the Loyalist Volunteer Force, a splinter group with a burgeoning drugs empire and no real desire for an end to violence.

Hanvey's play presents the intractable difficulties of this situation through the swiftly unravelling friendship of two young UVF men. Chris (sympathetically played by the author) is about to become a father and wants better for his child than a gangster world, ruled by money. Nick Storton's cagey, conceited Pinky, is bitter with frustration. The leadership in Belfast forbids fighting the LVF because it does not want to lose political credibility. So how is Pinky to stop these rivals from robbing his restaurant as they try to raise the money for a massive consignment of cocaine? And does his creepily manipulative plan mask an even deeper deviousness that demonstrates the extent to which, in the new mercenary dispensation, words like "loyal" and "loyalist" have been further debased?

There are implausibilities in the over-plotting of the piece. It turns on the fact that Chris's heavily pregnant partner Danielle (a far too healthy-looking Francesca Dymond) is a secret debt-ridden junkie who, to get her fixes, is forced to give sexual favours to Leon Bearman's repellent, power-crazed LVF dealer. In the most brutal scene in Jessica Hrabowsky's well-acted, if jerky production, we see the latter mercilessly beating her into miscarriage. The psychology and behaviour of Danielle - why she has become dependent on drugs and how she has managed to keep Chris in the dark for so long about her habit - remain a convenient blank. But while it is badly weakened by lack of emotional texture, Justice does have the smell of reality, a good ear for abrasive dialogue, and an impressive moral passion.

To 20 August (020-7837 7816)