“How did you kill these chickens?”

There are certain movies that seem to exist solely to demonstrate exactly why a particular actor or actress is a movie star. The magnitude of their performance eclipses whether or not the movie is good or bad and, more than anything else, becomes the primary reason to seek out the film. This is almost the case with Captain Fantastic and Viggo Mortensen, but it isn’t a feat that manages to fully come together.

As the titular Captain Fantastic (albeit only referred to as such in a roundabout way, as “my fantastic man” by his wife in flashbacks, and as captain of the bus he drives), Ben Cash, Viggo Mortensen is the patriarch of a brood of six. The family lives off of the land, hunting wild beasts with knives and arrows, and reading books like Middlemarch and Guns, Germs, and Steel after dinner. This idyllic existence is shattered by the suicide of their mother (Trin Miller), who has spent the last few months away from them in hospitalization, and the resulting question of custody. “We will go on living in exactly the same way,” Ben tells his children, but we know that’s not going to be true.

While the spirit of the movie — as free as its primary characters — is admirable, the constant tirades by the Cash family against typical society grow repetitive and lose their impact as a result, even as a device to show the difficulties in processing grief. It doesn’t help that every character besides Mortensen’s is a caricature or an archetype, e.g. Ben’s middle son (Nicholas Hamilton), angry and rebellious, and thereby given the typical teenage, “I hate you!” outburst, or Ben’s frustrated, “normal” sister, who even Kathryn Hahn can’t save from sounding shrewish. The only characters who manage to escape this trap are Ben’s youngest children, Zaja (Shree Crooks) and Nai (Charlie Shotwell), solely through the earnestness of their performances, and Frank Langella as Ben’s father-in-law, again a case of the performer managing to transcend their cut-and-dry material. On top of that, the mannerisms of the Cash brood — bordering on the quirky twee-ness that most would use to stereotype Wes Anderson’s work — never fully give in to the fantastical (no pun intended), making the whimsical conclusion of the film all the more perplexing.

The strengths of the movie come in individual moments — when the silence of the woods breaks into a joyous noise reminiscent of Spike Jonze’s Where the Wild Things Are, for instance, or the quieter beats in which Ben contemplates what is actually best for his children. In that sense, Captain Fantastic plays like a series of vignettes. The problem is that they don’t quite coalesce. Director Matt Ross manages to put slight twists on each of the expected story beats, but not with enough grace to make them feel less clunky, and the film’s simplistic way of addressing mental illness is only exacerbated by the big part that it plays in the narrative.

Mortensen is a worthy actor to carry a moniker like Captain Fantastic, but the same can’t be said for what’s been built around him. His performance shines, but there’s not enough around him to catch that light.