Rioult, once a prominent member of Martha Graham's company, is a fluent dancemaker in the mainstream modern dance tradition, and his 1995 Wien, which I saw several years ago, presents a compelling vision of Ravel's Valses Nobles et Sentimentales, even though it offers Balanchine's La Valse no strong challenge. But I find it difficult to watch Rioult's Black Diamond, set to Stravinsky's Duo Concertant, without having to brush away intruding memories of Balanchine's exquisite pas de deux to the same music. The conflicting visions may stem from how Rioult uses the music. Balanchine, for instance, emphasized the silences between the short, diverse pieces in Stravinsky's suite for violin and piano as preparations for change; the performers simply walk away from the onstage musicians they're listening to and get set to dance. Rioult makes the silences part of a fairly unvarying choreographic texture.

The jutting, darting qualities of the music as well as its shimmer may have been what suggested diamonds to Rioult, an image he conveys through faceted movement by two sleek women. Penelope Gonzalez and Posy Knight wear transparent black tops and pants over black bras and trunks, and each stands atop a large cube, the equivalent, perhaps, of a jeweler's velvet display case. Although the design (abetted by David Finley's cool, clear lighting) doesn't seem integral to the movement, it grips the eye.

The choreography is exacting. While remaining in place, rarely even twisting or turning, the two women thrust their limbs and angle their torsos along different linear paths, as if emitting rays. Sometimes one (or both) comes off her platform to the floor in front of it, and at one point we see their poses tiered, overlapped—Knight on her platform, Gonzalez on the step leading up to it. The choreography doesn't fully acknowledge Stravinsky's contrasting rhythms. The women's every move is deliberate, and only once, for a few seconds, does Gonzalez acknowledge a sprightly tune with quick little steps.

Rioult plays more daring games with familiar scores in his 2006 If By Chance and his new Exp #1—tinkering with the music itself. The earlier piece is performed to Jacques Loussier's interpretation of Mozart's Piano Concerto #2. "Interpretation" means that passages from a straightforward piano-and-orchestra recording of the Mozart morph into jazzy variations and back again at the drop of a shoulder or the swing of a hip. However, the ebullient dance for four bare-chested men in tights and four women wearing pretty, midriff-baring dresses by Pilar Limosner doesn't make major distinctions between the two style of music. In a carefully controlled summer-of-love atmosphere, Rioult emphasizes choreography for couples (male-female and same-sex—all four pairs often moving differently at the same time) and varies these with unison patterns and passages in which the dancers skim or leap across the stage (sometimes with steps borrowed from the Graham lexicon). When I think back on the piece, I can't quite grasp the point of the musical-choreographic mix (or figure out why some of the dancing looked a little rushed or rough around the edges).

In Exp #1, violent, eerie selections from Autechre's Amber simply cut out at the end of certain sections, and excerpts from J.S. Bach's Sonatas for Violin and Harpsichord take over. Whatever dramatic idea Rioult is working with, it remains maddeningly mysterious, but the piece contains some fascinating passages, and the dancers perform it excellently. Finley's lighting is crucial. In the opening sequence, Brian Flynn, Michael Spencer Philips, Robert Robinson, Jane Sato (terrific in everything), and Anastasia Soroczynski, invisible in blackness, stick their limbs into a crossbeam of light so that their hands and feet seem floating, disembodied. Later, the two women and soloist Gonzalez traverse the stage in a similar beam; at times, they seem—magically—to fly (the male arms that make this possible remain invisible in the surrounding darkness).

Marcus Jarrell Willis marvelously embodies the idea of disembodiment all by himself. Pinned in a spotlight, he jerks and shudders, his shoulders, head, and torso rolling at odds with one another. He leans back, advancing and retreating simultaneously. He behaves as if he's having trouble keeping his footing and pauses to watch his hands twitch. After a brief blackout, he reappears in the same place, flanked by the others, who copy his movements like photoshopped duplicates and then disappear. Later, a follow spot searches for Willis, finds him working his body in a corner of the stage, blacks out, picks him up somewhere else; he's unperturbed, still engaged in creating weird beauty.

So who is Gonzalez in all this? She's the Bach person. The harpsichord speaks for her. Alone onstage, she appears both predatory and vulnerable. When she eventually joins Willis for a duet, their bodies angle oddly around each other. In the end, the others again move into individual pools of light, and the curtain comes down.

Enigma is a vital part of the illusions dancing creates. It's engrossing when moments in a dance stir up multiple and memories, visions, and associations. But sometimes a dance, like this one, seems to be trying to tell us something. Not being able to figure out what that something is can be frustrating—especially when the work flickers with as many provocative images as this one does.