I was concerned to see the main photograph used to promote Claire van Kampen’s new play, Farinelli and the King. Appearing on the cover of programmes and on The Globe’s website, it features Mark Rylance—van Kampen’s husband and the play’s star—staring down solemnly at some shaky-looking candles. His character, King Philip V of Spain, is presumably contemplating mortality or his own madness. The image suggests a weighty production with its lead actor at his most serious and sententious. I’m pleased to report that the play itself is a lighter and less pompous affair.

Transferred to the Duke of York’s Theatre after a highly successful two-week run at The Globe earlier this year, Farinelli and the King tells the story of the famed castrato’s time in Spain in the late 1730s. It works hard to build up a sense of its two title characters as parallel figures: both reigning supreme in their respective domains; both wounded, torn between the experience of private sorrow and the awareness of public duty. But the King and the castrato are also united by a recognition of their own absurdity. The King’s mental illness is accompanied by wit and well-deployed obscenities. Farinelli sings him back to his senses, at least for a time, but his greatest accomplishment is in bonding with the man rather than changing him.

The play follows in the footsteps of Samuel Adamson’s Gabriel—which also premiered at The Globe and was reviewed by Criticks here—in combining period drama with musical performance. Farinelli is played by both an actor (Sam Crane) and a singer (counter-tenor Iestyn Davies in this performance). When an aria is called for, one Farinelli becomes two, the dormant self sometimes taking the opportunity to wander the stage or instead to examine his renowned public persona. There is valuable insight here into the novelty of celebrity in the eighteenth century. Farinelli is alienated from his own success and his own voice, a common enough complaint from modern-day stars, but one which must have held more weight in a period when the concept of celebrity was itself new and unfamiliar.

I wonder, though, if splitting Farinelli the man from Farinelli the singer also has some rather less positive effects on the audience’s engagement with history. I can see that for practical reasons it was pretty much essential, and the arias themselves—mostly by Handel—are beautifully executed. However, something of the strangeness of the castrato’s lived experience must be lost in thus isolating the performing self. Sam Crane speaks throughout with the voice of a healthy adult male, and no attempt is made to embellish his presentation with the obvious physical disfigurements—abnormal height and limb length, distorted skull structure—which tended to be part of a castrato’s life. We lose sight of Farinelli’s bodily discomfort at the same time that we are asked to embrace a highly romanticised view of his musical gift. The castrato’s voice is such that he himself cannot fathom its workings and its meanings. It is the voice of another world, thankfully irrecoverable to us, but grieved for in van Kampen’s play all the same.

Historical accuracy is likewise sacrificed in other parts of the production, again with mixed results. In an early scene, King Philip’s wife, Isabella (Melody Grove) speaks to Metastasio (Colin Hurley) backstage at the London opera, the librettist assuming that she is just another of Farinelli’s infatuated female admirers. The misunderstanding and the moment of Metastasio’s eventual realisation make for good comedy, but it is hard to believe that the invitation to Farinelli would have been extended by the Queen in person, or that she would have wandered unaccompanied and unheralded into such an encounter. Her character is subject to embellishments later in the play too, as van Kampen toys with the idea of forbidden romance between Farinelli and the Queen. This presents us with an intriguing love triangle, shedding further light on the castrato’s curious sexual appeal and his painful bond with Philip. However, the play must ultimately retreat from the scandalous possibilities it introduces here; this isn’t the story that it wants to tell. Besides, these moments seem more than a little indebted to an entirely different eighteenth-century inspiration: the excellent film A Royal Affair (2012) has already depicted the attraction of a queen to the man brought in to cure her husband. It did so with much more historical justification. The reign of Danish King Christian VII (1749-1808) was publicly shaped by these issues in ways that King Philip’s was not.

Alongside such instances of historical infidelity, one also experiences the opposite problem at points in the play. Certain historical references—to the slave-trade agreement, the Asiento, for instance—feel shoe-horned into the dialogue in ways that detract from the authenticity of the performances. Most ham-fisted (pardon the pun) is an allusion in the play’s final scenes to that newly-invented culinary delight, the sandwich. These scenes are set later in the eighteenth century so the reference isn’t anachronistic so much as gimmicky—it doesn’t really tell us anything of value about the characters or about habits of consumption at the time.

Still, as a whole, the play offers a gentle and touching reflection on the relationship between music, medicine and monarchical power. The staging—which features some on-stage seating—strikes a good balance between intimacy and spectacle. The performances themselves are energetic, and Rylance gives enough space to his fellow cast members that the fortunes of the work in the longer term should not be inextricably linked to his name and reputation. I hope, then, that an edition of the script is published soon. Without this, there is a danger that a play so unusual and challenging in its combination of music and theatre may slip from view.

Farinelli & the King is at the Duke of York’s Theatre, London, until December 5th 2015.