The actress Famke Janssen plays against a few types in “Turn the River,” Chris Eigeman’s respectable debut as a writer and director. Still very much an arresting figure as an ex-model and more recently as an “X-Men” fanboy fantasy, Ms. Janssen slumps into jeans and a loose T-shirt to play a frustrated, small-town pool hustler and returning absentee parent. Typically, those characteristics are reserved for the men of the silver screen, but her character’s slightly desperate devotion to her son is what drives this film.

“Turn the River” might also be unexpected from Mr. Eigeman, an actor known mostly for delivering acidic and unsparing sarcasm. Some of that surfaces in the embattled fatalism of Kailey (Ms. Janssen), who seems to take for granted that she has to make a living on green felt (pool or cards). Shuttling from her home base in upstate New York to the city, she meets secretly with her 12-year-old son Gulley (Jaymie Dornan) against the rules of a separation agreement, crashing either with pool hall owner Quinn (Rip Torn) or in her truck.

The bright, subdued boy, ever in private-school uniform, lives with his ornery father (Matt Ross) and stepmother (Lois Smith). At their rendezvous, Kailey greets him from yards off by getting to her knees and opening her arms wide, before inquiring about the particulars of his day. Her backstory remains persistently murky, but the massive chip on her ex-husband’s shoulder implies what their marriage might have been like; this is a bitter man who insists on needling his son over a piece of trivia by hauling an encyclopedia to the table.

“Turn the River” steers clear of pool-hall flash or routine defeatism as Kailey cooks up doomed-sounding plans to reunite permanently with Gulley. Sinking shots is a means to an end — cash — not for flaunting mettle or blustering. Indeed, it’s distinctly unappealing work; when two banker foes take her skills as an affront, they express their displeasure by knocking her flat. Nor is Kailey some magician with the cue stick. She vies with evident frustration against equally adept players in scenes shot with a matter-of-fact, lived-in feel for the game rather than with imposed rhythms.

Ms. Janssen embraces the vulnerability created by her character’s love for her son: Kailey moves between their fraught, emotional meetings and a world where someone who sees an angle will clear the table with it. She balances it with a flintiness that rears its head in the clutch, and she’s a sight more persuasive than Mr. Torn’s colorized refugee from a B-level fight picture who might as well be called “Pops.”

Without feeling like the centerpiece, Ms. Janssen’s grounded performance saves whole stretches of the movie. But the story veers off course when Kailey tries furtively to reclaim the boy, and the screenplay, despite a good ear for some bluntly stinging dialogue, plunks down backstory while leaving other aspects of the characters and the non-pool portions feeling hastily sketched.

Kailey’s plan to abscond with Gulley to Canada with fake passports and a gun makes about as much sense as it should from someone who doesn’t think out all her moves in advance. But the movie’s final chapter, which features a police standoff, plays like a misstep, coming from a different place than the decision, for example, only to imply the physical abuse inflicted by the boy’s father. In terms of films by actors plopping into the director’s chair, Mr. Eigeman’s entry is more considered than most, but the trouble spots remain.