Bash, Trafalgar Studios, London<br/> IWitness, Finborough, London<br/> Postcards from God, Jermyn Theatre, London

Sex and violence are a familiar pairing but, as Neil LaBute has realised, love and violence are even more disturbing and no less realistic. In the monologues of Bash (one has two people, but each speaks as if alone), three murderers try to explain what drove them to acts they themselves don't understand. All are, like violence, as American as apple pie.

Reactions to LaBute's work are an interesting test of not only the playgoer's sensitivity but his (and I mean "his") honesty. More than one male reviewer has stated that the character who kills his baby daughter after his job has been taken by a woman has done so for fear of being unable to provide for her. Better than any feminist author, LaBute makes us smell the petrol-fume stench of incipient violence that pervades the air around young men, and that can erupt in flames when combined with weakness - either that of another who must be crushed so they can confirm their manhood, or by their own terrifying surrender to the beloved. One of the murderers is a woman who has been driven to kill by love, but we never doubt that she should not be the one on trial.

All of the actors in Tamara Harvey's revival of these 1999 plays have caught their very ordinary characters' mixture of the appealing and the annoying. Harry Lloyd as the college boy with love in his heart and blood on his shirtfront, and Jodie Whittaker as his starry-eyed date, do something more - they make our own hearts stop as they gently, smilingly intertwine innocence and evil. Everyone's American accents are superb, but these two would fool Henry Higgins.

The latest work in Neil McPherson's imaginative tenure at the Finborough, IWitness is more impressive for the production than the play. Set in a prison cell, the drama by Joshua Sobol (author of Ghetto) is based on the true story of Franz Jagerstatter, an Austrian who was guillotined for refusing to serve in the Nazi armed forces. Franz, a motorcycle-riding mechanic, is no gooey pacifist but a stern, stubborn Christian with no need of priests, certainly not the one sent to reconcile him to the company policy of class-bound conformism and power worship. It is his "duty" to resist immoral authority, he says, scowling, like a railway employee who ignores orders to skimp on safety measures.

IWitness has moments of tension and fury, but these are undercut by a lack of plausibility. Given his beliefs, could his threat of violence ever be more than a demonstration of principle? When Franz is brutal to his clingy girlfriend, saying he wants to be free, are we supposed to see a desperate need to be loved as domestic fascism?

But, if the text is not always persuasive, the actors under Michael Ronen's direction are painfully realistic, from Mel Raido as the almost creepily implacable Franz to Natalia Tatarka's sensitive portrayal of his young daughter, trying to understand a situation that seems stranger than her childhood games of make-believe.

With The Sound of Music in the West End, and now Postcards from God, can a musical about Soeur Sourire, the singing nun who topped the charts with "Dominique" be far behind? I wouldn't rule out anything after seeing Myra Sands as Sister Wendy Beckett waft around the stage, eyes and mouth open in wonder at the rapture of art. With a backing group of four younger nuns making the sign of the Cross in time to music, Sister Wendy offered homilies such as "If we always knew what to do, there'd be nothing to learn" and "Very little in life is black and white", the latter rather contradicted by everyone's costumes.

When the paintings Sister Wendy elucidates come to life, they make far more startling observations. John the Baptist may be just a head on a dish, but that doesn't stop the old spoilsport reproving Salome in song: "The Baptist turned in deep disgust, / Repulsed not by her beauty but her lust." Other numbers were the kind we have all heard before, even if we've been locked in a nunnery for 40 years: "No matter what you do,/You can't deny it's true:/There's no one else like you." Between Sister Wendy telling us how wonderful art is, and her followers telling us how wonderful Sister Wendy is, Postcards is less a drama than a love feast, and our heroine's one lesson in art appreciation is the verbal equivalent of aromatherapy massage. I have higher hopes of the forthcoming all-singing, all-dancing version of Black Narcissus.