Hercules is one of Handel's enigmatic later works, suspended in the dramatic no-man's-land between opera and oratorio. The work's English text and choral-heavy composition align it with the unstaged Biblical blockbusters; yet the pagan subject matter and frankly sensual treatment of jealousy and madness belong to the far less improving realm of Italian lyric theatre.

Aidan Lang's fidgety production has a foot in both camps and a grounding in neither. He keeps the chorus onstage almost continuously, yet neglects to endow them with a gestural language to justify their presence. The costumes invoke statuesque classical drapery, yet the inhabitants are incapable of standing still. Instead, they go for little strolls, cravenly drawing focus from the da capo arias. Eric Owen's Hercules even joshes about during the ritornellos, mugging it up for laughs. It seems an extraordinary decision to programme such an intensely static work and so signally fail to trust it.

These distractions are especially annoying as the musical preparation, under the guidance of Harry Christophers, is exceptionally good. Christophers' own band of period specialists, the Symphony of Harmony and Invention, make a thrilling, febrile sound in the pit, and the cast is distinguished by two brilliantly matched sopranos in Yvonne Howard and Gillian Keith.

As Hercules is largely peripheral to his own drama, it's really the story of the conflict between his beautiful conquest and his embittered wife. Keith and Howard provide the voices of innocence and experience: Keith's tone as pure and fresh as the water that bubbles up so plentifully around these parts; Howard chestier but magnificently secure in the florid expulsions of Dejanira's madness.

This is baroque singing and playing of the highest order. A pity the production around it is such a Herculean labour.

· In rep until July 25. Box office: 0845 1272190.