The intensity of the “twins connection” is explored, to great dramatic effect, in the German/Swiss film “My Little Sister.” Gripping performances by Nina Hoss and Lars Eidinger map out the close bond and interlocked fates sister and brother display as one of them faces a terminal illness.

Lisa (Hoss, of “A Most Wanted Man” and “The Audition”) is a playwright struggling to write from the backwater Swiss city where her husband (Jens Albinus) is the headmaster of an exclusive boarding school for the children of potentates and oligarchs. But the move there and raising two small children are relatively minor distractions. Her twin brother, Sven (Eidinger, of “High Life” and “The Clouds of Sils Maria”) has been sick.

We meet them as she picks up her brother after a Berlin bone marrow transplant. He has lost much of his hair, so she provides a wig. And being theater folk, their first stop is a rehearsal. Sven was to play “Hamlet” again for a famous director who also happens to be Lisa’s ex (Thomas Ostermeier). Only a much younger actor is rehearsing the part.

“I didn’t get a transplant to watch my understudy,” Sven pleads, in German with English subtitles.

Lisa presses his case because she sees how much her brother needs this, needs a reason to push through to some sort of recovery. Herr Direktor equivocates, because “no one wants to see that.”

Lisa’s got a plan. She’ll stay here, maybe the entire family will move back to Berlin. Plainly their scattered mother (the great Marthe Keller) can’t take care of him.

“I can’t take care of myself,” she grouses, perhaps a little tipsy. “And look at you! You give me the creeps!”

Sven leans on “My Little Sister” (born mere minutes later) Lisa literally and figuratively as she tries to plan their way out of this.

But nothing is settled in Berlin and there are complications back in Switzerland, which bringing her brother into won’t help.

Hoss lets us see Lisa’s surface control and barely hidden panic in the early scenes. As events conspire to disrupt her “plan,” she starts to lose it. As her marriage suffers and family is shoved aside in her all-consuming attempt to help her brother physically and psychologically, she breaks down in fury and despair.

Eidinger adeptly captures a man who is putting it all in his earnest and intrepid sister’s hands, but who collapses into panic attacks as he enters those famous Kubler Ross “five stages,” realizing the limits to his sister’s support even if he barely thinks of her in his own worsening state.

The acting fireworks of “My Little Sister” flare up, but co-writers/directors Stéphanie Chuat and Véronique Reymond give their stars a glorious moment of grace, storyteller Lisa calming panicked Sven by telling him the tale of Hansel and Gretel, spicing it up a little for entertainment value.

The way these two play that scene, in a movie where dialogue is spare and emotions raw, tells us everything about their characters’ relationship, letting us see in a moment that this can’t be the first time she’s done that, because even though she’s the “younger” sibling, plainly she is the rock among the two.

“My Little Sister” may tell a simple, sad story, but it has everything we treasure in great screen performances. And Hoss, acting a full range of emotions in three different languages (German, French and English) moves herself front and center into the ranks of the best screen actors of her era.

MPA Rating: unrated, nudity, sex, profanity

Cast: Nina Hoss, Lars Eidinger, Jens Albinus, Thomas Ostermeier and Marthe Keller

Credits: Scripted and directed by Stéphanie Chuat, Véronique Reymond. A Film Movement+ release.

Running time: 1:40