When thirteen-year-old naval cadet Ronnie Winslow is expelled from Osborne College for the theft of a five-shilling postal order, his disgrace sparks a public and political uproar which will change the lives of those involved forever. As the drama escalates, the impact of the case loses all proportion to its small beginnings, and Ronnie's guilt or innocence, the nature of his crime, and the future of his family is swallowed up in the pursuit of an ideal and the spectacle of a legal tussle.

Birmingham Repertory Theatre, under the direction of Rachel Kavanaugh, haven't skimped on the traditional setting, providing a delicious chocolate box of an Edwardian set - a drawing room cluttered with ottoman and chaise longue, and Madeira served in tiny glasses. The first half of the play rattles along at a grand pace. The mood is energetic, the dialogue sparkling, and a cast of interesting characters is quickly being developed. Aden Gillett plays a wonderfully stern but good-humoured pater familias in Arthur Winslow, and the interplay between this fond father and his sardonic, intelligent suffragette daughter (Dorothea Myer-Bennett) is a highlight of the play. Timothy Watson's arrogant but principled barrister Sir Robert Morton dominates the stage as an engaging anti-villain, and Misha Butler does a pleasing turn as the largely oblivious Ronnie. Everyone is on their mettle, the language is lovely, and it all moves beautifully towards the climax of Sir Robert's preliminary cross-examination of Ronnie.

After this glorious pivotal moment, however, the energy of the playwright, and consequently of the cast, seems to dwindle somewhat. There's so much potential for serious drama: each member of the household finds their future and security threatened and the family faces ruin; but many potentially dramatic moments pass rather quietly by, weighty social issues are attractive window dressing, and the deeply-felt demands of personal morality and honour are treated as light social comedy. Austen pulled it off, but Rattigan doesn't have Austen's depth - although some hilariously pointed one-liners are delivered to great effect - and while the characters are promising, most avenues of potential tension are left unexplored. That said, I'm not sure the play is any the worse for it; not everything has to be hand-wringingly meaningful, and important subjects can appear subtly and incidentally in a work designed principally to entertain. Unfamiliar with both the play and the details of its background, I found it quite a treat to see despair denied at every turn.

In spite of its faults this is a funny, interesting, hugely enjoyable play, a cosy, feel-good drama, which, if you care to look deeper, can also be thought-provoking. You could take the whole charming confection as a comment on society's inability to deal with serious matters. Public ridicule, thwarted hopes and looming penury can be dismissed with a wave of the hand amid the sensational pleasures of a trial and questions in the House. Or you might decide that the widening ripples caused by Ronnie's trivial problem foreshadow the coming of a war whose destructive scale will soon dwarf its slight beginnings - almost as if the characters know that in a few short years their troubles will have been wiped out by something far more significant. So why worry about the future? Blow the house deposit on cappuccino and head down to the Playhouse for a well-crafted play which can be profitably unpicked, but which at heart, is designed to be enjoyed.