Shakespeare may not have been Montague, Capulet, Gloucester, Lear or Leontes, but his children certainly caused him grief. His only son died in boyhood. His younger daughter hitched her wagon to one of Stratford's wilder citizens. And marriage to the eminent physician, John Hall, did not stop scandal striking his elder one. In 1613, three years before the dramatist's death, Susanna sued a certain John Lane for slander after he publicly accused her of "runinge of the raynes", ie, a bad case of the clap, and having an affair with a haberdasher called Rafe Smith.

Was she guilty? A church court in Worcester declared not. But Peter Whelan, author of The Herbal Bed, suspects that the truth may be subtler, more complex, you might say more Shakespearean. She was guilty and not guilty. She hankered for the passionate Smith, and would probably have succumbed to him while her coldly principled husband was out on a call, had not the family servant made a fateful if Feydeauesque entrance into their love nest amid the marjoram and thyme.

Whelan's foray into speculative history needs a little trimming, at least in the early stages, but mostly remains as absorbing as the reviews from Stratford suggested last May. Towards the end, when Stephen Boxer's wily, wintry vicar-general is quizzing the nervously assembled parties, the piece takes on the grip of a courtroom thriller. But its point, interest and fun mainly derive from the sight of Shakespeare's daughter demonstrating her father's skill and resourcefulness when it comes to concocting a dodgy plot and making everyone believe it.

All the characters, from David Tennant's feckless, volatile Lane to Liam Cunningham's dourly well-meaning Hall, are made of what the Bard once called "mingled yarn, good and ill together". Its twin subjects are human contradiction and the evasions, fibs and fixes that enable marriages, families, medical practices and just about everything else to work. It is also about the puritanism that Dr Hall is prepared to compromise but Boxer's icy inquisitor will clearly embrace until the last cavalier disappears and Shakespeare and the theatre follow him into the oubliette.

This is an intelligent, enjoyable evening, and, thanks to Michael Attenborough's direction, a pretty well-acted one. If Teresa Banham's Susanna is comfier and less flustered than she should surely be, Joseph Fiennes comes into his own with a performance of boggling anxiety and bug-eyed confusion. And what of Shakespeare, who made a guest appearance in Whelan's equally excellent The School of Night? Sadly, the evening ends as he is about to be carried into the Hall home, suffering from the ailment his daughter does not have. But at least this means we do not have to see his raynes runing. It is, after all, his runing braynes that matter.