Sentimental and sympathetically-acted, actor-director Chiwetel Ejiofor’s “The Boy Who Harnessed the Wind” immerses us in Third World subsistence farming and the struggle just to have enough to eat in poor, corrupt countries in the developing world.

This Around the World with Netflix film, based on a true story, takes us to rural Malawi in Africa and introduces us to customs, rituals and the difficulties of life that is lived, harvest to harvest.

But when you title your film “Boy Who Harnessed the Wind,” you’re giving away the climax, unless you realize that you cannot make that your climax. Ejiofor’s movie teases and never lets us forget exactly where it’s heading. And it uses an almost unforgivable amount of its running time taking us where we know it is going.

William (Maxwell Simba) is a young teen growing up in Wimbe, a village where the corn is grown by hand and survival is measured in the baskets of dried maize you have in your larder. His father Trywell (Ejiofor, of “Twelve Years a Slave”) works the land he bought with his brother. But as the film opens, that brother dies. Trywell’s control over how the land is cultivated and guarded against flooding is in jeopardy.

Still, he’s got a couple of bright kids. Older daughter Annie (Lily Banda of TV’s “Deep State”) is waiting to get into college. Their mother (Aïssa Maïga of the French films “Paris J’taime” and “Cache”) insists on it. William is on a similar track. It’s just that their local school isn’t free, and Dad’s “after the harvest” isn’t going to cover tuition that’s due now.

Ejiofor teases “the solution” to their problems before all those problems — government corruption and indifference, drought and flood cycles, lumber exploitation, a romance tugging Annie off her path — are laid out in exacting and somewhat laborious detail.

William is the in-demand tinkerer in Wimbe. Everybody brings their radios to him to fix. And as he rummages through a nearby junkyard, we see the wheels turning in his head as he picks up this old battery or that half-broken water pump. Someday he’s going to discover the word “dynamo,” but we can already see the lightbulb flickering on and off over his head.

Ejiofor milks the cascading crises piling up on this family for all they’re worth. When Trywell looks at his boy and informs him “No one is coming to help us, you have to be a man, now” (in English and Chichewa with English subtitles), we can see William straining at the bit, dying to try out his big idea on his old man.

That spoiler-title and long, teasing storytelling style hamper the film, making “Boy Who Harnessed the Wind” a classic 90 minute movie hidden 113 minute one, and the story arc a classic wait-too-late-to-get-to-the-point melodrama. The “Eureka” moment should have come earlier, perhaps written into a race against the clock to make things work before people starve, or an exploration of how life was forever changed by this Big New Thing.

The “Boy” here has the reins, has the wind and starts to piece together what he’ll need for his harness. Ejiofor needed to let him have it and find more of a movie out of what came afterwards.

Rating: TV-PG, violence

Cast: Chiwetel Ejiofor, Maxwell Simba, Aïssa Maïga and Lily Banda

Credits: Scripted and directed by Chiwetel Ejiofor, based on the book by William Kamkwamba and Bryan Mealer. A Netflix release.

Running time: 1:53