Like a cross between a Charles Dickens novel and “Ripley’s Believe It or Not,” the story of Violet and Daisy Hilton is both tragic and almost incomprehensibly strange.

Born as conjoined twins in Brighton, England, in 1908, the identical girls spent their youth in subjugation, exploited and brutalized by managers who made a great deal of money promoting them in carnivals and on the stage.

“Bound by Flesh,” an exhaustive (and sometimes exhausting) documentary by actress-director Leslie Zemeckis (spouse of director Robert Zemeckis), is a cradle-to-grave story about two spirited survivors who could never escape a life on display.

Zemeckis traces Violet and Daisy’s youth with sensitivity and care. We learn they were abandoned by their mother and raised by two generations of brutal managers, who beat them and kept them impoverished, friendless and ignorant about the larger world.

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But Zemeckis also drifts from her subject, offering overly extensive context for America’s unseemly taste for “freak” sideshows in the early 20th century. (Cineastes will remember the Hiltons having roles in Tod Browning’s unsettling 1932 drama “Freaks.”)

The story picks up when the sisters free themselves from their keepers and embark on years of vaudeville stardom as dancers and musicians (they performed with both Bob Hope and Charlie Chaplin.) Needless to say, tabloid-like tales about their individual love affairs, marriages and one unwanted pregnancy raise curiosity.

One senses while watching “Bound by Flesh” that things are not going to go well for the Hiltons as years go by. It’s true — and terribly sad.

Tom Keogh: