From the moment the aspiring poet Donal Davoren fails to deny being a member of the IRA, in order to perpetuate the romantic delusions of the only attractive girl in his tenement, we know Sean O'Casey's The Shadow of a Gunman is going to end in tears.

But, as Jon Pope's faithful production at Glasgow's Citizens Theatre carefully emphasises, Donal's is by no means the only finger on the tragic trigger. Obviously, culprit No 2 is Donal's room-mate Seamus Shields, a disillusioned Republican who hawks cutlery and braces on the mean streets of 1920 Dublin and who is in a state of Beckettian stasis over trying to leave his own "hopeless country". He's also at least as erudite as Donal, on more than equal terms in their spats over literature and politics. But, bright as he is, he would prefer to believe that his sinister acquaintance Maguire is off to Sligo for a few days to collect butterflies than that he is off to do a job with the Boys. He's also too frightened to question whether the contents of the box Maguire asks him to mind might be more explosive than cutlery samples.

As Donal and Seamus, Lalor Roddy and John O'Toole make a credible pair of "likely lads" out of their depth in a civil war where matters of loyalty and identity are no laughing matter. Their fellow residents are ultimately no less culpable and just as colourful, from Anna Healy's malapropic Mrs Henderson to James Ryland's cringingly obsequious Mr Gallagher. O'Casey suggests repeatedly that some of the major difficulties faced by his characters (and by Ireland) stem from a negative (in the photographic sense) perception of the world. Seamus, for example, complains bitterly that jokes are taken seriously while serious things are taken as a joke.

Taking O'Casey's cue, Pope formalises this central duality by playing the first half as an early situation comedy, "lightening" the proceedings by cramming his cast into a shallow, screened acting space at the front of the Citizens' main stage.

In the second half, situation comedy gives way to situation tragedy, the screen has gone, and the depth of Kenny Miller's stage design is finally allowed to lend its full weight to the production. The design itself also has a subtle ambiguity about it - Donal's and Seamus's shared room is decked out in authentic naturalistic detail, littered with old newspapers and piles of books, while behind and above them towers an expressionistic tenement wall, weeping with black grime, into which are set, like mournful eyes, two long windows framing the night's stars.

With Miller's backing, Pope and his cast conjure up an unnerving climate of romance and fear in which comic errors produce tragic consequences, and where the gunman's shadow distorts everyone's vision.

n `The Shadow of a Gunman' is at the Citizens Theatre, Glasgow, to 28 Oct. Booking: 0141-429 0022