There is something inherently fascinating in the drama of a personality receding into a degenerative neurological condition, as demonstrated by such successful films of recent years as “The Father,” “Still Alice” and “Away From Her.” A first directorial feature for actor Celyn Jones and cinematographer Tom Stern, “The Almond and the Seahorse” promises a similarly compelling tale. Rebel Wilson and Charlotte Gainsbourg play disparate women both coping with domestic partners suffering escalating consequences from traumatic brain injuries (or TBI). 

But intriguing as that sounds, this overstuffed narrative never quite finds its footing, wobbling between cutesy comedy and tearful histrionics. Its erratic progress fails to fully realize central characters, despite the multinational cast’s efforts, or even shed much cogent light on the diagnostic theme. Based on a stage play, the film feels sufficiently cinematic to (mostly) hide that origin. Yet the patchy storytelling suggests an awkward compromise between two mediums that, rather than effectively expanding a theatrical conceit, leaves “Almond” both hectic with melodramatic incident and burdened by too much theatrical language. IFC Films is opening the Wales-shot feature on 100 U.S. screens as well as VOD platforms Dec. 16.

Archaeologist Sarah (Wilson) is trying to hang onto her marriage with Joe (Jones, who originated that role onstage 12 years ago). But like Elvis, he has more or less left the building: An unspecified “illness” two years prior is laying waste to his long- and short-term memory, stirring abrupt mood swings, childish impulsive behaviors, and so forth. At a point when they’d intended to start having children, she is instead turning into his minder. Already a full-time caretaker is Toni (Gainsbourg), who had to abandon her architecture practice after she and her spouse were in a car accident. Now former cellist Gwen (Trine Dyrholm) suffers acute disorientation, sometimes not even recognizing her partner or home. 

The consulting expert for both patients is Dr. Falmer (Meera Syal), an authority on TBI whose facility also houses advanced cases. When Sarah and Toni find themselves forced to admit they can no longer help (or handle) their afflicted mates, institutional residency becomes inevitable. 

“The Almond and the Seahorse” — named after similes oft-used to describe impacted parts of the brain in such cases — has an ultimately ambitious scope, showing over a long haul how life goes on despite the de facto loss of a still-living significant other. But like most things here, the closing grace notes are more recognizable for their good intentions than notable for their emotional impact. Capable actors are stuck trying to flesh out characters that feel like sketchy constructs, with little detail in the writing between rote career designations and hysterical outbursts. When two leading figures suddenly “find each other” at the one-hour mark and have an affair, it seems ludicrously contrary to everything we’ve learned about them as individuals. 

While the directors and their solid tech/design collaborators manage to avoid staginess much of the time, dialogue nonetheless increasingly has a theatrical feel, with people too often speaking like position papers or spouting forced life wisdoms. It’s also problematic that some scenes likely invented to make things more “filmic” — as when middle-aged Toni dances her frustrations out amid twentysomethings at a rock club — are so gratuitously shoehorned in, they could be excised without any impact on the story whatsoever.

The result is no one’s best work. European heavyweights Gainsbourg and Dyrholm expend firepower on a script (by Jones and original playwright Kaite O’Reilly) that doesn’t provide them sufficient foundation. Wilson, billed as making her dramatic debut here, actually gets stuck with a fair amount of sitcom-ish comedics, which alongside too many excuses to cry and scenes in which she pieces together a skeleton (to remind us Sarah is an archeologist) add up to more of an earnest but middling star turn than a credible character. 

Jones the co-director overindulges Jones the thespian, in a performance that could have used a restraining hand. Syal plays the chief medico here with a superior smirk much more off-putting than comforting, while subsidiary figures embodied by Alice Lowe and Ruth Madeley strike antagonistic notes they get too little screentime to make sense of. 

This isn’t a bad film; it’s polished enough on the surface to provide a degree of satisfaction for those seeking a telepic-level “problem drama” with a novel hook, attractively shot for the big screen. But one suspects whatever strengths “The Almond and the Seahorse” had onstage have been significantly diluted in a translation that stretches clumsily to suit its new medium, and can’t quite stick the landing.