[2] Based on true events during German occupation of Poland, the film tells about Leopold Socha, a sewer worker in the Polish city of Lwów.

He used his knowledge of the city's sewer system to shelter a group of Jews who had escaped from the Lwów Ghetto during the Holocaust in Poland.

In the Lvov ghetto, Jews face persecution and humiliation by German SS men and collaborating Ukrainian police.

[4] One winter morning, Socha sees an SS man aiming at Mundek and cleverly kills him with a Jewish smuggler's help.

[4] The film concludes with the final caption:[4] Leopold Socha died on May 12, 1946, saving his daughter from the wheels of a speeding truck of the Red Army.

The last survivor of the group, Krystyna Chiger, published a memoir of her experience, The Girl in the Green Sweater: A Life in Holocaust's Shadow (2008).

Between 1987 and 2009, nearly one hundred films were made in Poland, a number testifying to the eruption of repressed memory and response to the intensifying debate.

[13] Ella Taylor of NPR wrote In Darkness "satisfies for the intensity of the performances and for the artful contrasting of life on the teeming streets of L'viv with life and death in the dim, rat-infested sewers", adding that it "is often a thrilling adventure picture — as if Anne Frank had found an Inglourious Basterd to help her make The Great Escape".

[14] Ty Burr of The Boston Globe called the film "a harrowing Holocaust tale, but one that speaks to humankind's capacity to endure, to fight on in the face of terrible cruelty", adding that Holland "elicits taut performances from a strong cast".

[16] Todd McCarthy of The Hollywood Reporter said this "harrowing, engrossing, claustrophobic and sometimes literally hard to watch […] robust, arduous drama is more ironic and multi-faceted than most such tales and should be well received by the considerable art house audience worldwide partial to the subject matter".

[17] Joe Morgenstern of The Wall Street Journal said this "brave epic" film's "suspense, derived from a true story, is excruciating and inspiring in equal measure".

[19] On the other hand, Roger Ebert of the Chicago Sun-Times dismissed the film as redundant and inferior to Schindler's List which was "more entertaining" in his view.

[20] Michael Atkinson of the Village Voice claimed that "Holland does skirt the ethical entrapment of Schindler's List (over-lionizing the Aryan rescuer)", adding: "It's not fair, but there it is: We've been here before.

[22] the Polish districts of citi David Edelstein of New York Magazine wrote: "In outline, In Darkness is a standard conversion melodrama, but little within those parameters is easy.

"[23] Mick LaSalle of San Francisco Chronicle called it "an extraordinary movie, and somehow good art […] a gripping piece of history and also an exploration into the mysteries of the human soul", and gave it "the highest recommendation".