THE curtain rises on Black-adder-land — epicene monarch, black-clad baddie, hooped ladies and preening hero — and you think, hmm, three hours of trying to turn opera seria into comedy could be a bit wearing. Worst fears aren’t entirely realised, but if you don’t trust Handel to hold an audience with a serious exploration of relationship and motivation, why bother?

The London Handel Festival has brought us some notable rarities from among the man’s operas, and this one too has seldom been seen; but if the performance falls short, it’s not because the piece is rubbish.

Its premise is that Massimo is plotting to kill the emperor Valentiniano, who raped his wife, using the emperor’s daughter’s love for the military hero Ezio to accomplish this. Naturally there are many other complications involving the daughter Fulvia and the emperor’s sister Onoria; the troubles these patricians cause themselves are wryly commented on by the robust pleb Varo.

Metastasio was a thoroughly competent librettist who established character and plot before lighting the emotional fireworks, but the first scene-setting act is precisely the one William Relton’s staging fails to engage with, preferring a pervasive visual jokiness — Romans played as English Georgians with 20th-century body language, an elaborate coffee-drinking shtick — to actual engagement. It might have worked in last year’s Sosarme, but here the tone is misjudged.

As a result — and not helped by a sturdily metronomic orchestral performance conducted by Laurence Cummings — the fact that a vocal turn of some class is developing passes unnoticed. The opera should really be called Fulvia, and Elizabeth Watts sings the role with a deepening passion that excavates her torments brilliantly.

Watts can do the trilly soubrette but there is much more to the voice — rounded, athletic, surprisingly fiery, and lacking only the last bit of control. Anna Grevelius as lovelorn Onoria has a nice mature mezzo, Tim Mead’s Ezio is a delight, focused, flexible and expressive, and George Matheakakis as Varo has fun with Handel’s most vivacious idiom — the opera becomes more like Water Music in Act III because that’s when George II was expected to turn up.

The production’s other major hole is the characterisation of Massimo, a bad hat of intricate, introverted rage who here is blandly motiveless.

Given space, Handel’s music does the job with brilliant, understated precision. When cluttered by business intent on stating the obvious, it can become pointless.

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