Molly Bloom’s 2014 memoir “Molly’s Game” was more of a tell-some than a tell-all. In the book, the former freestyle skiing Olympic hopeful discussed the accident that derailed her athletic career. Mainly, she wrote about her improbable career running a pricey, underground poker game in Los Angeles and, later, in New York City, where she ran afoul of mobsters, drugs and the feds, who arrested Bloom as part of a mafia investigation.

Her book named names, up to a point. Leonardo DiCaprio, Ben Affleck and Tobey Maguire were among her A-list regulars, blowing through cash like Kleenex. But her memoir left a lot out, and that’s where writer-director Aaron Sorkin’s movie “Molly’s Game,” taking place before and after the publication of her book, comes in.

It’s a good, brash biopic. For the first hour it’s very nearly terrific. Jessica Chastain plays Molly, driven hard by her taskmaster father (Kevin Costner), growing up in a fiercely competitive family. Years later in LA, Molly gets a job working for an industry bottom-feeder (Jeremy Strong, clearly fresh off a Giovanni Ribisi weasel workshop) who hosts a weekly poker game. Molly’s duties include recruiting high-rollers who might want to pal around with movie stars over huge, steaming piles of chips. Michael Cera plays one such star, euphemized in Sorkin’s script as “Player X.” The names of the real-life gamblers in Bloom’s book have been changed, presumably, to protect the litigious.

Like Sorkin’s Oscar-winning “Social Network” screenplay, this one’s a shrewd welter of flashbacks and present-day scenes. Everything builds to the moment when Molly determines whether to plead guilty to the feds’ charges. Along the way she locks horns and trades high-speed banter with her silky-smooth attorney. Idris Elba is a godsend in this role, one that requires a fast mouth (it’s Sorkin), a lively wit and fire in the eyes. That last quality’s particularly helpful when there’s a ton of legalese to carve up and serve to the audience.

Chastain’s aces in “Molly’s Game,” capturing both the Colorado free spirit and, as Elba’s character says, “the Cinemax version” of herself once she establishes a reputation as the notorious “poker princess” riding for a fall. “I’d always figured sophistication would be easy to learn if I ever needed it,” Molly reckons in voice-over.

The “fall” part rarely is as easy, or as fun, as the “rise” in a fact-based chronicle of ambition, greed and moral compromise. In the second half of this longish film (140 minutes with credits), Sorkin struggles to accommodate Molly wrestling with her father issues, and her mission to have “power over powerful men.” Here the writing gets blunt and a little less artful. These later scenes hark back to some of the lesser sequences in Sorkin’s “Steve Jobs” script. The best of “Molly’s Game,” however, is more on the “Social Network” level, edgy and rhythmic. This is Sorkin’s feature directorial debut, and I’m happy to say it doesn’t look that way.

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‘MOLLY’S GAME’

3 stars

MPAA rating: R (for language, drug content and some violence)

Running time: 2:20