Aaron Sorkin is a mercurial talent, a writer with a crackerjack sense of momentum, but also one given to going off the rails without a firm external governing influence. Knowing this, I’d worried that his directorial debut could prove the undoing of “Molly’s Game.”

It turns out that Molly Bloom herself leavened Sorkin’s tics and played to his natural strengths, enough to turn “Molly’s Game” into a crisp, engaging, fun film.

The subject matter – Bloom’s autobiographical tale of how she went from near-Olympian skier to would-be law student to the organizer of her own high-stakes poker rings, twice over – thankfully limits Sorkin’s opportunities for explicit political soapboxing.

That said, it wouldn’t be a Sorkin script unless he worked in a few appropriate digs at the system that exploited Bloom. He does this through stirring speeches delivered pitch-perfectly by Idris Elba as Charlie Jaffey, a fictional character based on Bloom’s real-life lawyer, who takes her case in the film because he shares her impeccable integrity.

What keeps this film grounded, however, is the power of Bloom’s authorial voice, through dialogue and voiceover monologues delivered briskly and charismatically by Jessica Chastain as Bloom herself. Bloom is presented here as an instinctive and quick learner, driven by killer ambition to show up the relatively underwhelming men in her life, even as she refuses to sell out their secrets to prosecutors.

“Molly’s Game” is an odd hybrid, one part step-by-step process narrative on how to establish your own loyal room of high-roller poker players, and another part rhetorical fencing match between Bloom and Jaffey over how much she can retain her ethical principles when faced with the prospect of losing all her money and being sent to prison.

Be warned again, this is still Sorkin, a man who believes subtext is for cowards, as seen when Jaffey has his daughter read Arthur Miller’s “The Crucible,” just so he and Bloom can reference it by name when debating her chosen stance.

Also, you’re not getting a strong female character from Sorkin without a heavy ladling of daddy issues, delivered here by Kevin Costner as Bloom’s overbearing, philandering psychologist father. It helps, though, that Costner himself denies that this is the source of Bloom’s drive or talent.

Between “Molly’s Game” and “Miss Sloane” in 2016, Chastain is settling into an effortless groove of playing professional women who hold their own against powerful men.

Likewise, just as Scarlett Johansson was born to deliver Joss Whedon’s dialogue in Marvel’s first “Avengers” film, so too do Chastain and Elba seem like machines calibrated to speak in Sorkin’s idiosyncratically rapid-fire, high-IQ dialogue without making it sound stilted or unnatural.

I’d have to do more research to determine how much the real-life Molly Bloom deserves the goodwill that Chastain’s portrayal earned from me, but I am curious to see what she’ll do next, because I don’t doubt it’ll be big.

Movie lover Kirk Boxleitner writes about Jefferson County government and other news and features, when he’s not watching movies. Contact him at kboxleitner@ptleader.com.