Resplendent in pastel-pink trouser suit, Pam welcomes us to her seminar.  We're in a church hall, somewhere in small-town America; judging by that suit, it must be the 1980's.  And we're there because we're concerned parents – worried about a godless game that's sweeping the nation's youth.  We're the "good BADD", Pam reassures us… we're Bothered About Dungeons & Dragons.

Don't worry though: you don't need to have played the iconic dice-rolling game to enjoy this show.  There are plenty of in-jokes for the initiated to savour, but the main thrust of Carrie Marx's script is a parody of evangelical America, or at least of what we imagine evangelical America to be.  The scene's set by a ludicrous run-down of Satanist ills, ranging from women's lib to Ozzy Osbourne – and Pam soon progresses onto a practical guide, for those concerned that teenagers' monosyllabic grunts are a symptom of demonic possession.  Along the way, she describes some gloriously misguided original research, and even experiments on her own audience (a bravura gimmick that's made all the more rewarding if you've seen it coming all along).

Pam's character is beautifully realised and, for all her flaws, is likeable enough to want to spend an hour in her company.  She's an awkward orator, filling her lecture with forced rhetorical questions and unnatural switches in tone – but the off-guard moments are the golden ones, as her face contorts in comic horror at some imagined sin.  There's no cheap knowingness to Marx's portrayal, so the illusion she creates is all-consuming; when the audience broke into applause at an overblown "emotional revelation", it wasn’t Marx we were congratulating, but Pam.

If I'm honest, some of the repeating jokes get old – Pam's habit of distracting herself, for example, is funny the first time but grows wearying later on.  The extended periods of audience interaction dragged a little too.  Naturally enough, random non-actors plucked from the crowd can't command the stage like Marx can; it just about worked on the night I attended, but I've seen enough examples of this particular trick to know it won't work every time.

Yet there's something more serious beneath this hilarity, as Pam's own story leaks out gradually over the course of her lecture.  It's no great surprise, but it's affecting enough to land substance to the play, and Pam's occasional flurries of unguarded honesty are invariable highlights in the script.  It takes a while to cotton on to what we're hearing – on the night I attended, some profoundly serious lines drew misguided instinctive laughs – but I'm glad that Marx resists the allure of a sudden shock, giving us time to fit the pieces together ourselves.  The only downside is the oddly low-key ending; I wanted and expected more of a hurrah, and I'm left suspecting that Marx hasn't quite decided what thought she'd like to leave us with.

First and foremost though, BADD is a well-worked laugh-out-loud comedy, with obvious appeal to geeks like me but enough universal reference points to transcend its niche.  If you've ever rolled a d20, you won't want to miss it.  And if you haven't, see it anyway; BADD is good for everyone.