For a while it seemed that Harriet Tubman’s face was likely to appear earlier on the twenty-dollar bill that on any movie screen, but with the controversial postponement in a decision on the new currency Kasi Lemmon’s docu-drama about the escaped slave turned activist for abolition who famously led other runaways to safety—the first since the NBC mini-series starring Cicely Tyson four decades ago—appears first. “Harriet” is a worthwhile if rather conventional effort—a strong, solid biography of an historically significant figure that’s educational, inspirational and emotionally potent.

It is also, after a fashion, a superhero movie, though not of course in the most banal terms. The actions of Tubman were in truth heroic, in terms of her own remarkable journey northward from a Maryland plantation to the free city of Philadelphia, the numerous missions she undertook afterward to lead others along the route she blazed (earning her mythical status under the name “Moses”), her service in the Civil War and her later advocacy of women’s suffrage. But director Kasi Lemmons has also chosen to emphasize the visions that Tubman had—she attributed them to divine inspiration—that were, as shown here, instrumental in helping her avoid capture—and save those following her as well—during the long trek to freedom.

Lemmons and co-writer Gregory Allen Howard (whose original script she extensively reworked) also accentuate that “superhero” feel by shaping the narrative in terms of a personal conflict with an exceptionally nasty villain—the plantation owner who makes it his special task to recapture his “property” and thereby destroy the legendary status that has built up around “Moses.” And by infusing the film with passion and poetry (the latter provided in collaboration with cinematographer John Toll and composer Terence Blanchard), Lemmons gives it a broodingly mythic quality.

The film begins with Minty (Cynthia Erivo), as Harriet is called on the plantation, kept in slavery, along with her mother (Vanessa Bell Calloway) and sister, by plantation owner Edward Brodess (Michael Marunde) despite his great-grandfather’s will freeing them. When Edward’s son Gideon (Joe Alwyn) inherits the plantation, he decides to sell Minty despite his feelings for her; since the sale would permanently separate her from her husband John (Zachary Momoh), a freedman, she decides to flee, assisted by her father (Clarke Peters) and the local pastor (Vondie Curtis Hall), who is in league with the underground railroad. She must, however, leave John and her sister Rachel (Deborah Ayorinde) behind.

Almost miraculously, Harriet evades being recaptured by Gideon and reaches Philadelphia, where she is welcomed by abolitionist William Still (Leslie Odom Jr.) and taken onto the staff of her boardinghouse by Marie (Janelle Monáe). She insists, however, on returning to Maryland to reconnect with her husband and assist Rachel to escape, and though she is frustrated in both those purposes, she helps others—including her brother—to make their way north, frustrating Gideon and his mother (Jennifer Nettles), as well as notorious slave hunter Bigger Long (Omar Doresey) and his young assistant Walter (Henry Hunter Hall), largely as the result of the prescience about their plans her visions provide.

As the reputation of the person called “Moses” grows, Gideon becomes more and more obsessed with capturing the elusive figure even before realizing it’s Harriet. She, meanwhile, has become an integral part of the Underground Railroad, though the passage of the Fugitive Slave Act makes even Philadelphia unsafe, requiring her and her fellow escapees to flee further north or be returned to servitude. During the Civil War she contributes to the Union military effort, at one point even leading an armed force to allow slaves to escape, and a postscript briskly details her activism up to her death in 1913.

Lemmons covers all of this in what might be termed expert docu-drama style, with excellent production and costume design by Warren Alan Young and Paul Tazewell. Wyatt Smith’s editing lays out the events in crisp chronological sequence, keeping the action clear down to the inevitable final confrontation between Harriet and Gideon (satisfying, however accurate it might be).

The film nonetheless depends in great measure on the performance of screen newcomer Erivo, who endows Tubman with passion and gutsiness. To be sure the film literally bathes her in a glow of virtual sanctity, making her indomitable even in the face of the most hopeless-seeming circumstances. But though the scent of hagiography is palpable, Erivo’s commitment is so strong that she gives even the most calculatedly melodramatic moments a strong sense of reality.

Nor is this a one-woman show. Alwyn, Odom and Monáe are all fine, but Peters, Calloway, Curtis Hall and Momoh offer especially vivid, if fleeting, vignettes. And as the rascally fellow who at first tries to capture Tubman but then becomes her faithful follower, Hunter Hall will certainly be a favorite, especially with younger viewers.

And they should be encouraged to see “Harriet.” Tubman remains a genuine American hero who hasn’t received the recognition that should be her due—but, with the current administration’s decision to postpone (and perhaps cancel) her appearance on U.S. currency—is likely to persist. Even if all it did was to make her story available to a wide audience, Lemmons’ film be doing a valuable service; as it is, bolstered by Erivo’s exceptional performance, it’s a stirring drama as well as a good history lesson.