One actor. One setting. No back story. No dialogue. One hell of a movie.

“All Is Lost” is a survival-at-sea story stripped to the essentials, a muscular, Hemingwayesque film with compelling emotional drive. Here, less truly is more.

First there’s a terse opening narration. In a note to his loved ones, Robert Redford apologizes, confessing that “All is lost but soul and body and a half-day’s rations.” Then we meet him eight days earlier, traveling alone aboard his trim 40-foot sailboat, the Virginia Jean. Her skipper is nameless; he’s called “Our Man” in the end credits. He is far from shipping lanes on the Indian Ocean. Not far enough. A half-submerged cargo container collides with Our Man’s craft, opening a man­hole-sized gash near the water line.

It’s a hell of a wakeup call. Our Man is intelligent and resourceful, laying repair patches over the wound and sealing them with waterproof epoxy. The seawater in the cabin is mopped up and the voyage resumes.

There is a big drink of whiskey to celebrate his victory over the elements.

But trouble is a pack animal, and it attacks again and again. Our Man’s confidence and self-sufficiency are tested to the limit, and so are our nerves.

Like a chef crafting a superb meal out of simple ingredients, writer/director J.C. Chandor demonstrates how much may be accomplished with a minimalist approach. With a subdued score by Alex Ebert and keenly observant, unobtrusive camerawork by Frank G. DeMarco, Chandor creates a neutral backdrop to showcase his solo star.

It’s doubly impressive contrasted with Chandor’s dialogue-heavy 2011 debut film, “Margin Call.” The hyper-verbal ensemble drama, a financial-disaster movie, earned Chandor a best original screenplay Oscar nomination. Here, pictures tell the entire story.

Though the film isn’t weighted down with thesis statements, its theme is clear. Man lives a solitary existence, subject to the relentless, unforgiving forces of nature. Does one best give meaning to that dilemma by valiantly battling on until the last gasp, or by accepting inevitable fate with dignity? There’s a surplus of fine survival stories currently in theaters — “Gravity,” “Captain Phillips,” “12 Years a Slave” — but none has the radical purity of this engrossing nautical drama.

Redford is not acting in this nonspeaking role so much as being. He moves from one urgent task to the next with authority. We look over his shoulder as he improvises fixes for his weather-battered, increasingly vulnerable boat. The camera setups reinforce a feeling of intimacy as he works. The film demonstrates how to revive drenched electronics and how to distill potable water from seawater and sunlight. To repair the radio antenna atop the tall main mast, he must haul himself to dizzying heights. We rise with him, sharing his vertigo-inducing perspective, bristling gooseflesh every perilous foot of the way.

Our Man is pragmatic, intensely focused on what he must do to survive another day. So are we. Forty-five minutes in, as Redford watches from an inflatable life raft as the Virginia Jean sinks, he has an irrevocable hold on our sympathy. He truly is Our Man.

His battle with the elements is punishing. The internal battle against physical injury, hunger, exhaustion and despair is tougher, and Redford communicates it eloquently. At 77, after a legendary career, he has delivered his defining performance.