Mahler's Conversion, Aldwych, London

Psychological Faustian pact in cartoon form

In one of his earlier plays, Taking Sides, Ronald Harwood put the eminent conductor, Wilhelm Furtwängler, in the dock on the charge of having remained professionally active in Hitler's Germany. His new play, Mahler's Conversion, subjects another great conductor (and, in this case, composer) to ethical scrutiny. Here, the questions raised are less to do with the responsibility of the artist to society than with the duty of the artist to himself.

The biographical basis of the piece lies in the fact that on 23 February 1897, the Jewish Gustav Mahler was baptised a Roman Catholic. Less than three months later, he made his triumphant debut, conducting Lohengrin as the new director of the Vienna Court Opera – a dream post that anti-Semitism would otherwise have denied him. The two events cannot be unconnected, but writers on Mahler differ over whether he paid a terrible inner price for his apostasy. Harwood's hectic, clunkingly unsubtle play melodramatises the religious conversion into a kind of psy- chological Faustian pact, a fatal decision that would come back to haunt the maestro when he had lost his job, his younger daughter, his health and his domestic content.

There is certainly potential in this story, though whether Mahler's life is the ideal vehicle for an exploration of the penalties of burying your true self is debatable. His ambiguous status was not, after all, a secret; it did not compromise his art, nor did it stop him suffering from anti-Semitic prejudice.

Harwood's supposed insights into the conversion (that Mahler, on the run from the nightmare of the eternally wandering Jew, was searching for a home and that his creative ego yearned for faith in an afterlife) are served up in a piece that often resembles a grotesque parody of the bio-play at its worst. Characters shout soundbites of theme and gobbets of exposition at one another.

As Mahler, Antony Sher begins as a cartoon of the genius played as frustrated force of nature and ends as a caricature of the genius as a lonely, broken and emasculated titan. Given the size of the theatre and the pumped-up material, Greg Doran has little choice but to turn in an overblown production.