Tallchief was the first American ballet star, and she thoroughly broke the mold of what a ballerina could be. She had Native American and Scotch-Irish heritage as well as an unusual admixture of power and grace. She was Balanchine’s third wife (from 1946-1952), and her years as muse numero uno generated a remarkably diverse legacy—including the bold, untamable Firebird as well as the regal, delicate Sugar Plum Fairy. Her influence was great on season kickoff lineup: she originated a lead role in the neo-classic “Caracole,” the lusty Coquette role in “Sonnambula,” and the airy, pseudo-sylph ballerina lead in “Scotch.” I was thinking about her throughout the program, which I chose to attend on the second night of the season, when Unity Phelan, another dancer of great range, debuted in “Sonnambula.” Phelan was dancing the Sleepwalker role, though she could just as fittingly have been cast as the Coquette. Like Tallchief, who code-switched easily between sylphs and sirens, Phelan is carving an interesting path through the rep.

She also carved an interesting path through “Sonnambula.” The Sleepwalker role is an odd one, though everything about “Sonnambula” is odd—down to the many destabilizing 5 and 9 count phrases in the music (by Vittorio Rieti after themes of Vincenzo Bellini). Somehow, the ballet traffics in high drama while withholding its actual plotline. It involves murder, lust, and betrayal—but the details are fungible. Almost immediately, a love triangle is established between a rich Baron, a Coquette, and a Poet who crashes their party. But then the love triangle shifts and centers around a new woman when the Poet engages with the mysterious Sleepwalker. Upon finding out about their dalliance, the Baron stabs the Poet to death. (The Sleepwalker is pegged as the Baron’s wife in Balanchine’s Complete Stories of the Great Ballets, though never in the program.) Much is left to the dancers to decide; thus, casting is a major factor. “Sonnambula” can read wildly differently depending on who is tippy toeing across the boards. And the Sleepwalker role doesn’t change hands too often, so new blood is an event. Young blood is an even bigger event, as the role is generally the province of older ballerinas. Though there is precedent for both seniority and youth: Balanchine created the role for Alexandra Danilova, who was 43 at the time, and revived it for Allegra Kent, at 22.

The puzzle with this particular cast (who were all debuting) was: why was Phelan’s Sleepwalker—young, beautiful, pliant—wandering the halls of the mansion while her older husband (Jared Angle) caroused with a Coquette (Georgina Pazcoguin) closer to his own age in the ballroom? When the married couple is equally senior in years, and the Coquette is a hot young thing, it is rather obvious why the wife won’t get dressed for dinner and is instead roaming around in her nightgown in a stupor. It’s tempting to overlay Balanchine’s biography onto the tale: he cast his ex, Danilova (she was his romantic partner from 1926-1933, and is considered his unofficial second wife), as the crone in the attic and his young flame Tallchief as the Coquette (they were married six months before “Night Shadow” premiered, she was 21 and he was 42). But to consider Balanchine only in the Baron position is facile. There are several fascinating psychological doublings happening in “Sonnambula,” and I suspect Balanchine identified with both male characters—likely much more so with the dreamy, artistic Poet who sparks to an unattainable muse. And though by definition a Poet’s medium is language, this is a ballet, so the audience has no evidence of his verse. What we do see, however, is the Poet guiding and shaping the movements of the eminently malleable Sleepwalker—i.e., choreographing.

The Poet’s chance encounter with the Sleepwalker shifts his focus from his loins to his intellect, from a state of lust to one of contemplation. After his sexual urges are frustrated in the ballroom, his soul ignites at the sight of a woman who operates on a higher plane—literally, as she almost never comes off pointe. The real drama in “Sonnambula” is not the battle over a woman—either woman—but the conflict between the spirit and the flesh, dreams vs. reality, art vs. life. Older Sleepwalkers—their movements more brittle, their legs less high—inherently symbolize a sort of monomaniacal dedication to art over reality. They have chosen to keep dancing around on their toes in defiance of what their toes (and backs, and hips) might be saying; it is the ultimate commitment to mind over matter. But even within this framework, interpreters have a wide range of options. Younger Sleepwalkers, however, have an even bigger challenge, requiring yet more imagination. From Kent on, this contingent has historically been up to the task, and Phelan was no exception.

Phelan portrayed the Sleepwalker as more automaton than dreamer, madwoman, cuckold, or ghost. She appeared robotic, emotionally detached from the world. She didn’t play it at all like a Gothic horror story, like some (the best of this camp was surely Janie Taylor, with her thrillingly creepy poltergeist take). Phelan seemed alive and well on the outside, but utterly dead on the inside. She was nearly catatonic; perhaps she was on Xanax. She reminded me of Catherine Deneuve in Belle de Jour, unable to square her complicated inner desires with her bourgeois reality, and so she was sleepwalking through her home life in a repressed state. Phelan’s mind seemed to exist elsewhere, and if you replaced her candle with a cell phone it would have been apt. She was plugged into something else. Phelan was a Sleepwalker for the current generation, and it was poignant.

Her castmates, however, needed to get their stories straight. Harrison Ball, debuting as the Poet, came to life in Phelan’s presence. Before her arrival, however, things were murky. He and Pazcoguin, as the Coquette, had little sexual chemistry. When he entered, it seemed to trigger some deeply traumatic memory for them both; I wondered what terrible thing had occurred in their past. I was reminded of Pazcoguin’s stint in “Cats” on Broadway, but here she was channeling Grizabella’s ballad “Memory” rather than her own playful kitten role. This choice was hard to reconcile with the levity of the blindman’s bluff party games, their handsy pas de deux, and even her decision to inform the Baron of the Poet’s kiss with the Sleepwalker. You’d think she’d have been happy that Ball could move on from whatever horrors they’d lived through; their romance seemed definitively over. In response, Angle wisely chose the route of the stiff upper-class lip as the Baron. When the Coquette started to reel and emote at the sight of the Poet, Angle basically rolled his eyes and retired to the billiards room to wait out her dramatic episode. But this only worked up to the end, when his jaded apathy didn’t quite mesh with his crime of passion. Until Phelan came on the scene, the ballet belonged to Cainan Weber as the Harlequin sideshow, with his sensational split jumps.

Sterling Hyltin, who danced the Sleepwalker the night before, gave a beautiful performance in “Scotch Symphony,” Balanchine’s travelogue ballet. She was a wisp of a pink cirrus cloud floating across the heath. Her partner, Anthony Huxley, was also great—especially the pinpoint precision of his tours to four corners in the finale. Both were perfectly suited to their roles—it showed that they’ve danced James and the Sylph in the full-length “La Sylphide” many times. But the central “Scotch” ballerina role is not all fairy. At the end of the pas de deux, Huxley put his arm around Hyltin they casually sauntered together. She ditched the mystical disappearing act and became a Scottish lass strolling with her beau. (It was almost the inverse of the “Sonnambula” ending, in which the Sleepwalker claims the Poet in death and carries him up to her tower.) In “Scotch,” Balanchine gave Tallchief the opportunity to display her otherworldliness and then come back down to earth. Olivia MacKinnon was zippy and sassy in the soloist role, which also pulls in different directions. Instead of wearing a corseted romantic tutu like the rest of the women in the cast, Mackinnon wore a kilt and sporran like the men and jumped alongside them too. Her role is that of a tomboy, yet a flirty and swishy one. She was well-flanked by Alec Knight and a smiling, snappy Victor Abreu in a fill-in debut.

But it was “Divertimento No. 15,” the opener, that displayed Balanchine’s neo-classical lens at its sharpest. Though the dancers wore the most stereotypical ballet trappings—pert tutus, tights, and pastel tunics—it was by far the most radical work on the program. “Divert” is so insanely musical that it is borderline comical at times. As I watched the corps women do stately walks and then scramble through each other to a new formation to a musical flourish, I was thinking that the Trocks could spoof “Divert” without having to make too many adjustments. But “Divert” is so beautiful that its humor is tempered; it makes you smile, not laugh out loud. Though it is plotless, the tension between Balanchine’s playful wit and his streamlined classical aesthetic is plenty dramatic.

“Divert” was brilliantly performed by the entire cast, though I’ll give special nods to a few. Aaron Sanz and Davide Riccardo were clean and elegant in the Theme. Ashley Laracey’s soft and expressive upper body contrasted nicely with her crisp and precise lower half. And Tiler Peck is pure butter in the ballerina role; her ability to decelerate and accelerate in the middle of a string of chainé turns is mind-boggling. Ever since her debut in the role, she has really put her own stamp on the part. In “Divert,” the dancers have less dramatic leeway, yet more artistic freedom. Like in most of Balanchine’s masterpieces, the dancing speaks for itself—and thus the dancers can too. These are the ballets that let Tallchief—and the chameleons among the current crop—push themselves artistically in any direction they like.