Is there an actress around today with a more inscrutable yet expressive mouth than Anna Kendrick? Sure, she can flash her pearly whites like the best of them, sing quite well (as the three “Pitch Perfect” movies proved), and deliver a withering line as if she’s slicing one’s soul (“Up in the Air,” “A Simple Favor”), yet it’s her commissure, the line of her mouth when her lips meet, that truly captivates. Both upturned and downturned at the same time, it can be as impassive as a modern sculptor’s basic outline of pursed lips and as inquiet as a squiggly line.

Ms. Kendrick puts this “Mona Lisa”-like asset to effective use in the new movie “Alice, Darling.” As Alice, she portrays a young, urban professional in an emotionally and mentally abusive relationship with an artist named Simon (Charlie Carrik). His psychological manipulation and narcissistic neediness is manifested through comments on her weight, relentless texting when she’s not with him, and the like. 

When we first meet Alice, she’s already cracking up, coping when she’s alone by stringing her hair around her fingers, sometimes to the point that she pulls out strands in little puffs of anxiety. When two longtime friends, Sophie and Tess, invite Alice for a weeklong getaway at a lake house owned by Sophie’s parents, ostensibly to celebrate Tess’s birthday, the uneasiness continues. Conversation between the three friends is strained, with Alice withdrawn and barely eating anything. Her one escape seems to be running, which she does early in the morning while listening to self-help podcasts. Another release comes when she learns to chop wood, an activity she embraces so vehemently that it scares Sophie. 

Having lied to Simon that she was going on a work trip, Alice comes clean to both friends when he finds out where she really is. Unable to understand why Alice would lie about such a thing to her romantic partner, the two hide her wallet and phone so she can’t run back to him. Matters reach a breaking point in an excruciatingly intense scene featuring Alice in a bathroom, her hair once again her only exorcising recourse for confusion and distress.

The decision to take away her phone proves to be helpful, though, because soon the tension that has suffused the movie begins to diffuse. When Alice tells her friends how Simon treats her, it’s apparent they had sensed it all along. We finally get to see her having fun, in a scene where they go to a local bar and dance. This is as much of a relief to the audience as it is to Alice. When Simon appears at the house the next morning, though, she reverts to her passive personality, with her friends looking on disapprovingly.

As the concerned friends, Wunmi Mosaku and Kaniehtiio Horn anchor a movie that at times can feel too jittery, as their characters do with Alice. One wishes screenwriter Alanna Francis and first-time director Mary Nighy (daughter of actor Bill Nighy) had shown Alice before she met Simon, so we could assess her mental health unrelated to the relationship. Ms. Kendrick, for her part, hints at problems beyond her boyfriend trouble. During her scenes with Mr. Carrik, there are suggestions of sexual obsession and power trips that the filmmakers apparently were too timid to address directly.

A metaphoric subplot involving the search for a missing girl in the lake town mostly goes unexplored, with its shades of Atom Egoyan’s “Exotica” making me wish I were watching something as artful and discomfiting as that arthouse classic. Still, “Alice, Darling” relays not only a powerful message about harmful relationships and the responsibilities of friendship, but a knockout, completely unexpected climax. 

In this scene and in its coda, we see Alice in two different settings, one fraught and the other relaxed, yet Ms. Kendrick’s countenance remains essentially the same. Her eyes, forehead, jawline, and especially her mouth convey a range of emotions: fear, determination, discontent, anger, and finally hope. The images of her face are quite indelible, approaching the status of an ancient, mysterious idol.