Claire Van Kampen's play about the 18th-century castrato singer Carlo "Farinelli" Broschi - who gave up a glittering opera career to sing to an audience of one, albeit the King of Spain - could so easily have been one of those plodding bio-dramas.
But with the mercurial Mark Rylance as Spain's depressive monarch, together with an inventive production (directed by John Dove) that is at times like a concert, and the mesmerising countertenor Iestyn Davies (who on alternate dates shares singing duties with Rupert Enticknap), plodding this superb show is most certainly not.
The plot by Kampen (who is spouse to Rylance) fizzles somewhat in the second half. But, on the whole, this is a beautifully observed, cleverly told tale - previously seen at Shakespeare's Globe's Sam Wanamaker Playhouse - that glories in the therapeutic and civilizing effect of music on the troubled mind.