Principal men being in short supply, we've grown accustomed to the stream of male guests flown in to eke out Royal Ballet casts. Not women, though. It took an exceptional set of circumstances - the absence of Darcey Bussell, undergoing surgery on an ankle, the presence of Milanese guest partner Roberto Bolle, and the heightened expectations of a first-night Romeo and Juliet - to prompt the Royal to call up Alessandra Ferri, a one-time Royal Ballet favourite who defected to American Ballet Theater 18 years ago.
And what an inspired call that was. Ferri has none of Bussell's creamy line, still less the pretty face. Nor is she a cool dissecter of character on stage like Sylvie Guillem. What's more, she's 40, and MacMillan's Juliet is as gruelling as MacMillan roles get. Yet Ferri delivered a performance on Wednesday I will remember all my life. From the moment she scuttered on with her nurse in Act I, to her last agonised gasps as she crawled to Romeo's side to die, she sucked her audience into a vortex of newly quickened feeling with a force that wrung me out.
Yet at first the sheer onslaught of it prompted doubts. Was it nerves, or was Ferri trying too hard in her first encounter with Bolle's plushy dreamboat of a Romeo? Neither, I decided. We're just not used to that level of emotional verismo. At the Capulet ball the conscious naughtiness of being courted by one man and secretly encouraging another repeatedly sets her shaking in repressed fits of giggles. In the balcony duet her up-for-it excitement is so raw you want to blush. Here is none of your wide-eyed innocent. Ferri's Juliet is the 14-year-old of every parent's nightmare.
I always love it when ballet stops being photogenic and gets its hands dirty. And Ferri looks as if she's been crying for 10 hours from the post-marriage bed pas de deux on. Hollow-eyed, desperate, hair plastered to her skin with sweat - she's not a pretty sight as she contemplates the Friar's plan. And her hand shakes so much that she can't get the stopper out of the bottle. "Why do we put ourselves through this?" whispered my companion. Why indeed.
Ferri's intensity naturally raises Bolle's game, transforming him from Mr Terribly Nice to the kind of boy who might well break into a crypt, stab the first living person he comes across, and lug a corpse around like meat. In turn, Bolle is such a pillar of dependability that Ferri feels safe to dare more.
None of which changes the fact that MacMillan's ballet is desperately uneven. With its acres of padding and cheesy street scenes, true fans are only there for the duets. Birmingham's Royal Ballet Sinfonia, filling in while the regular band takes a holiday - hardly did Prokofiev any favours either. Conductor Barry Wordsworth got the fortissimo he asked for, but rather more dissonance than was written.
Musical honours of the dance week go to the young pianist Jason Ridgway, playing dazzlingly intricate Scarlatti sonatas on stage as part of Martin Lawrance's Grey Allegro, receiving its British premiere at The Place. Using dancers from Richard Alston's company (to which Lawrance belongs), the piece offers a crisp visual counterpart to the fingeriness of the music, as well as its formal devices, yet also hints at a vestigial emotional narrative that keeps you on the edge of your seat.
At 30, Lawrance has mastered tricks that floor mature choreographers: how to channel the gaze in a busy number; how to pace, how to dramatise endings and beginnings - and crucially, how to get tip-top performance from his team. In both Grey Allegro and Lost, an older piece, I was held so rapt that I kept on forgetting to breathe - some achievement in abstract, post-modern dance. Make no mistake, Martin Lawrance is going somewhere fast.
'Romeo and Juliet': ROH, London WC2 (020 7304 4000), to Sat