“Irena’s Vow” is a potent reminder that the world needs heroes — those brave enough to do what’s morally right even when the risks are great.

In theaters on April 15 and 16 via Fathom Events, the consistently compelling film is based on the true story of Irena Gut OpdykeI, who, during Nazi Germany’s occupation of much of Poland, put her life on the line in an attempt to protect a group of Jewish people from extermination. Astoundingly, she hid them right under the nose — literally under the feet — of a Nazi officer.

“Irena’s Vow,” which premiered in September at the Toronto International Film Festival, first existed as a play. Years after its 2009 debut off-Broadway, its writer, Dan Gordon, has adapted it for the screen, and, under the deft direction of Louise Archambault, the film is something greater in scale than a stage work performed in front of a camera.

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The movie is anchored by the measured performance of Sophie Nélisse as Irena, who also goes by Irene, and whom we meet in 1939 as she’s working as a nursing student at a hospital. Word arrives that Germany and Russia have divided the country.

“Poland is no more,” someone announces — moments before an explosion rocks the hospital.

Soon, like other Poles, Irena is spending her days contributing to the German effort.

“Work hard and no harm will come to you,” a Nazi tells her and others.

Work hard she does, but she isn’t cut out for factory labor and is reassigned as a domestic house laborer. She thrives in this new setting, where, along with cooking food that impresses the Nazis who dine there, her duties include supervising 12 Jewish workers in the laundry. She suspects many of them have exaggerated their tailoring skills to seem useful, and she assures them they all must do better for their sakes, as well as hers.

Because he’s been so impressed by her, Major Rugemer (Dougray Scott) informs her she is being moved again, this time to the villa into which he is moving and where he regularly will host parties for other high-ranking Nazis. She will be in charge of running the house.

Irena Gut Opdyke, portrayed by Sophie Nélisse, impresses Nazi officer Major Rugemer, portrayed by Dougray Scott, with her work early on in “Irena’s Vow.” (Darius-Irena Productions Inc.)

Shortly before this, she overhears an intimidating SS officer, Rokita (Maciek Nawrocki), tell Rugemer that soon no Jews in the sector will remain among the living. Already shaken by witnessing an act of near-indescribable Nazi heinousness in the streets, Irena decides she will hide her friends in the villa’s cellar, planning to make use of a brief window of time between when she gains access to it and Rugemer arrives to move them there.

From that moment through most of the rest of the film, as World War II rages on, “Irena’s Vow” is a largely nerve-wracking experience, as Irena and her friends face one challenge after another. To their credit, though, Gordon (“Passenger 57,” “Wyatt Earp”) and Archambault (“Thanks for Everything,” “One Summer”) never overdo it; as a viewer, you sense that most days in the characters’ lives are largely uneventful but that you are witnessing those that are anything but that. The film even contains moments of relative joy, such as when, early on in the precarious situation, the cellar dwellers help Irena prepare a feast for a party, Irena having insisted to Rugemer she needed no extra help in the house and needing to prove that to be the case.

Nélisse, whose film credits include “The Book Thief” and “47 Meters Down: Uncaged” but who may best be known for portraying the younger version of Shauna on Showtime’s “Yellowjackets,” does her finest work as Irena must portray an increasingly complex character and the situation around her evolves.

Sophie Nélisse’s Irena most play an increasingly complex role as “Irena’s Vow” progresses.” (Darius-Irena Productions Inc.)

Because the film is told from Irena’s point of view, “Irena’s Vow” does little in the way of character development when it comes to those whom Irena is hiding; we see them only when she is interacting with them. It is both understandable and a little disappointing.

As a result, one of the few other actors who gets to make much of an impression is Scott (“Deep Impact,” “Ever After: A Cinderella Story”). In his hands, Rugemer falls somewhere in the vast space between entirely loathsome and at least vaguely sympathetic.

We are treated to a couple of nice moments courtesy of Schulz (Andrzej Seweryn), who, many years Irena’s senior, imparts upon her some advice for navigating her new reality.

“You worry about you. You take care of you. You know only what you need to know,” he says, adding that she should be like a monkey — hearing nothing, seeing nothing and speaking nothing.

Fortunately for some, the real Irena — who, according to press materials for the film, was named by the Israeli Holocaust Commission as one of the Righteous among the Nations, a title given to those who risked their lives by hiding and saving Jews during the Holocaust, and the recipient of the Israel Medal of Honor — couldn’t live that way.

“Irena’s Vow” is a stirring tribute to her bravery.

‘Irena’s Vow’

Where: Theaters.

When: April 15 and 16.

Rated: R for some strong violence and brief sexuality.

Runtime: 2 hours, 1 minute.

Stars (of four): 3.5.

Editor’s note: This article was updated at 4:58 p.m. to correct the dates the film is slated to run in theaters.