The Dog in the Manger, Swan Theatre, Stratford-upon-Avon

The first play in the RSC's Spanish Golden Age season, The Dog in the Manger, is not only a delightful evening of old-fashioned fun, it's a fascinating opportunity to see how the 400-year-old play stacks up against the work of Lope de Vega's English great near-contemporary, in particular Twelfth Night.

Diana, the bitch of the title, is, like Olivia, a haughty spinster knocked flat by her passion for a member of her household. (At one point, literally - in a ploy to get him to break protocol and touch her, Diana sinks gracefully to the floor behind her beloved's back, emits a tiny cough, and whimpers, "I've fallen".) Like Shakespeare's, this comedy has a scheming servant who outwits the master, and his one-line reference to a past passion recalls Sir Andrew Aguecheek's wistful reminiscence,"I was adored once".

What's more interesting than the textual compare-and-contrast, however, are the psychological and social differences between the works of the two authors, and the different worlds they imply. Both may please the pit with cheeky servants and foolish aristocrats, but the public to whom Lope appealed dwelt in a society more rigidly stratified than that of England, more oppressive and gloomy. The only obstacle to Diana's marrying her secretary, Teodoro, is the Spanish code of honour, and her struggle with her sense of propriety is less engaging than the Shakespearean battles with a heavy father or reluctant lover.

Nor, in Lope's punitively prim Catholic country, is there any place for the bawdry that is such a rich source of humour for our poet. The only allusion to bedroom stuff is Teodoro's deadpan recap of Diana's tale of an imaginary friend who loves an employee: so, he says, your friend "desires a man beneath her, er, sorry, my lady. Poorly put".

The vigour of Laurence Boswell's production is the main reason for its success, though others are not far behind: David Johnston's sparky translation, with just a few jolly anachronisms; the sober-but-sumptuous design of Es Devlin - a floor crisscrossed with slashes beneath which subterranean fire burns, and costumes such as Diana's aubergine gown, tight-laced and jet-encrusted.

There's a splendid cast: Rebecca Johnson's charming Diana, Joseph Millson's dishy Teodoro, Simon Trinder's indefatigable Tristan, and the poignant, elegant Claire Cox as Marcela, the lady-in-waiting Teodoro dumps when he sets his eyes on the higher prize. (Diana wins her epithet by punishing Marcela at the start of the play for loving Teodoro, whom she herself will not yet stoop to conquer.) Teodoro's airy dismissal of this lovely, blameless girl is considered by Lope no impediment to our cheering him on. Both geniuses had the cynicism of the honest, worldly man, but Shakespeare, with his greater heart and greater art, added sorrow to his.

In rep to 2 October (0870 609 1110)