Steven Cantor's Dancer plays like a PBS installment of Behind the Music with ballet standing in for rock and roll—and that's not necessarily a bad thing. Like Mikhail Baryshnikov, Ukraine-born Sergei Polunin has an angular face, crystalline eyes, and the awe-inspiring ability to fly through the air with ease. His mother, Galina, claims he was so flexible from birth that it alarmed her nurse. He used that skill as a gymnast before switching to ballet.

To pay for his pricey schooling in Kiev, Polunin’s grandmother took a job in Greece and his father took one in Portugal. "That," says Polunin now, "is when fun was over." The working-class family pinned their hopes on him to the exclusion of everything else. It's not hard to understand why such kids go crazy when they get a taste of freedom, and that's what happens in London. If he's a star student, Polunin is also a party monster, but it doesn't prevent the 19-year-old from becoming the Royal Ballet's youngest principal.

Meanwhile, his family implodes with visa problems and broken marriages. By 2012, he's had enough and he walks away. The rest of Cantor's film tracks his attempts to find a place where he can be himself. It's a compelling story, up to a point, but Polunin 's personal life always remains off-screen. Though that may be by design, it leaves this portrait feeling frustratingly unfinished.