Following his claustrophobic debut “The Guilty” (remade, to lesser effect, by Antoine Fuqua), Swedish filmmaker Gustav Möller returns with a second feature that may expand its call sheet but is still confined in its approach to characters and settings. Trading out an emergency service center for a prison, “Sons” narrows in on a single prison guard and her attempts to exert control over a prisoner with whom she has a history with.
As played by Sidse Babett Knudsen (“After The Wedding,” “The Duke of Burgundy”), Eva is a career prison guard in a minimum security sector of a prison. Maternal yet firm, we see her day-to-day interactions with the prisoners, which include yoga and meditation sessions, as well as tutoring. Yet, when a new prisoner, Mikkel (Sebastian Bull) arrives, Eva requests a transfer to the solitary ward, for reasons the film isn’t in a rush to lay out. 
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There, Eva slowly turns into a more sinister figure, withholding Mikkel’s cigarettes and refusing to allow him to go to the bathroom. The reasons for this shift are made more apparent as the film progresses, including a tragic backstory involving her son, who was sent to prison and died there. But, really, Möller is interested in the way that power can shift between guard and prisoner, as Eva and Mikkel become locked in a battle over who can gain the upper hand. 
More schematically interesting than plausible, the film essentially isolates Eva and Mikkel’s interactions, creating a two-hander that explores the imbalance of power between the two, even if those interactions rarely feel rooted in reality. Too often, Eva is alone with a violent prisoner, allowed to withhold essentials from him, despite the constant presence of her hard-nosed boss, Rami (Dar Salim, “Guy Ritchie’s The Covenant”). 
Yet, even if the film strains credulity, it is still fascinating to watch as Möller unspools the reasons behind Eva’s torment. Tracking her character’s transition from a humane guard to a type of malignant presence in Mikkel’s life, Knudsen’s performance credibly showcases how previous trauma can change someone’s entire worldview. Bull is, perhaps, more one note, playing a psychopath who nevertheless cannot understand why this guard is out to make his life even worse. A mid-film twist that inverts the power between the two characters further showcases the despair that Eva is trying to contain. 
Aided by Jasper J. Spanning’s boxed-in cinematography, the prison is shot in a vérité-style that lingers on the day-to-day minutia of the guard’s and prisoners’ lives. Rarely do we leave the prison, suggesting that Eva is just as much a prisoner there as Mikkel. If anything, Möller seems to thrive in these types of contained settings, even if the reasons for keeping his characters there are stretched to the limits. 
When we finally do leave prison’s confines — on a day trip that Eva is forced into suggesting — the film’s titular interests clarify, as we see Mikkel’s mother (Marina Bouras) grappling with her own troubled relationship with a son that she cannot understand or control. Like much in the film, the parallels between these mothers (and sons) are unspoken. But, of course, there is a connection between Mikkel and Eva’s own son, even if the film withholds the reason behind that connection for way too long, effectively making the exposition a third-act twist that feels unnecessary. 
How these two characters circle each other and questions surrounding whether Eva will exact revenge are front-loaded. So much so that when the film’s thematic interests — about the cycles of trauma — clarify in the end, they don’t fully resonate. Instead, one is often left wondering how Eva was able to sneak around so much despite the constant surveillance in the prison. Even if “Sons” makes less logical sense than it should, it nevertheless remains a compelling character study  [B-]