But this is no ordinary drawing-room

drama. Friel, like Jan·c

.ek, has acquired a cloak of guile with advancing years. A lesser writer would have set the story in cloche period, borrowing copiously from Jan·c

.ek's fervent words and Kamila's clumsy locutions. Friel took the decision to depict Jan·c

.ek not in his time but in ours, as a spectre in the corner of a 21st-century rehearsal room where young members of a string quartet are wrestling with the score of Intimate Letters.

The device is extraordinarily effective, both dramatically and in terms of musical intuition. For the Jan·c

.ek we see and hear on stage is the Jan·c

.ek we have come to know through posthumous publication and musicological research. The nub of the play is the spectre's disputation with a dewy-eyed and apparently virginal doctoral student who is determined to nail the truth of his love for Kamila.

Friel, as an empathetic Angry Old Man, has no truck with romantic clichés that depict Leos

. and Kamila as Dante and Beatrice, lover and muse. His take is subtler and more satisfying. Without giving away too much of the play's resolution, Friel views Kamila as a myth of the composer's invention, a necessary fiction in which the old man found inspiration.

Not that she was physically unreal. Kamila was a dumpy housewife, sexually unattainable and cerebrally unstimulating. What the composer saw in her was a template, a blank page on which he could allow the imagination to run riot. What Friel sees in that connectionis something close to the secret of creation.

A severely private man - it is whispered that he will attend the London premiere but no one's quite sure - Friel opened Performances at the Gate in Dublin, where it split Jan·c

.ek followers into angry camps of romantics and rationalists. "I'd love to see fisticuffs in the bar at Wilton's," says Stein, who met Friel in Belfast when the playwright attended a choral concert of works by the director's wife, Deidre Gribbin.

"This is not a conventional play for a conventional theatre," Stein, founder of the Gate Theatre in Notting Hill, adds. "Brian uses words and musical quotations with a deftness we haven't seen since Tom Stoppard wrote Every Good Boy Deserves Favour, three decades ago."

The spectral part of Jan·c

.ek is taken by the versatile Henry Goodman, who has played Mel Brooks on Broadway and Gilbert and Sullivan at English National Opera; Rosamund Pike is Kamila; the excellent Brodsky Quartet, who have just recorded the work perceptively on their own label, will play Intimate Letters live during the course of the performance.

Apt as the Stoppard reference might be, Performances is as sharp a take on the social context of musical composition as any play I have read since Peter Shaffer's Amadeus - and that clever text captures more of the nature of musical relationships than most musicians will ever grasp. Performances is about essence more than appearance. It encourages us to look beyond the hissy gossip and accepts as natural law that gain in art never comes without those around the artist feeling the pain.

The ultimate tragedy in Jan·c

.ek's story was Kamila's - dead of cancer seven years after him, at 43. She uttered no reproach for anyone, least of all the moonstruck old man who plucked her from a crowd to grant this very ordinary woman the gift of immortality.

Performances is at Wilton's Music Hall, Grace Alley, Ensign Street, E1 (020 7702 2789), 3-15 July.