Did she fall, or was she pushed? The story of Amy Robsart, the neglected wife of Robert, Earl of Dudley, who was found dead at the bottom of the stairs at Cumnor Place while her husband cavorted with Queen Elizabeth I, has intrigued generations of balladeers and storytellers. The latest to fall under its spell is the composer Philip Cashian. With the novelist Iain Pears as librettist, he has written a one-act, 80-minute opera in which he speculates on one possible solution to the Elizabethan murder mystery - and I'm not telling you what it is.

The trouble, though, is that we're told rather too early on. In fact, we watch it happen. So don't go to Hammersmith expecting a thriller. Cashian's skill is to make the true mystery that of the human heart. His score, for Chroma's tiny ensemble of seven players, conducted by Tim Murray, is an electrocardiogram of Dudley's heart, torn between a wife he loves and a Queen he adores.

Counterpointing his own long lines, first of ennui, then of impassioned mourning, is a sinister spooking of percussion, and a tense cross-hatching of violin, cello, flute and clarinet, as the courtiers William Cecil and Sir Francis Walsingham play out their own equally dark and complex loyalties.

In Riverside's tiny Studio Three, the audience is drawn closely into this shadowy Elizabethan miniature. Bill Bankes-Jones, directing for the indefatigable Tête à Tête, makes powerful use of a space scarcely four paces long, and dominated by a live portrait of the Queen herself: a mute, immobile part for the actress Sibylla Meienberg, framed in a mock-up of the famous Darnley portrait, and omnipresent throughout.

The drama is all in the music, and in its spare, strong characterisations of the young wife herself, sung sweetly by Amy Carson; of a highly-strung Dudley, whose writing tests the tenor Andrew Rees to his limits; and of the engaging cameos of Phyllis Cannan as the servant Catherine, Robert Gildon as Cecil, and Roderick Earle as a powerfully sung, brooding Walsingham.

Box office: 020-8237 1111. Performances tonight, Fri, Sat and Sun

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