In “Molly’s Game,” Aaron Sorkin’s drama about a real-life underground poker ring that brought out the worst in the wealthy and famous, Jessica Chastain plays the game runner, Molly Bloom. A one-time Olympic competitor, Bloom finds her unlikely niche as something between cocktail waitress, crime boss and independent businesswoman — a powerful combination of don’t-touch sex appeal and coolheaded self-possession. What Sorkin wants to know is why this competent woman decided to make her living off men with such poor judgment, weak spines and broken morals.

The answer might lie in the question, but Sorkin — who wrote the screenplay from Bloom’s memoir and makes his directorial debut — strings us along through this highly entertaining film by dangling Molly’s “Rosebud” question before us. The film traces Bloom’s male-dominated life story, from her childhood under a strict father (an excellent Kevin Costner) to her testosterone-driven poker games and, finally, to the moment she needs a good lawyer (Idris Elba plays Charles Jaffey).

If you’re looking for a tell-all, well, “Molly’s Game” is more like a tell-some, dropping coy hints without ever naming names. Who’s the manager of the famous Los Angeles nightclub? The married rock star who begged Bloom for an affair? We’ll never know. Bloom did, however, name one regular player, Tobey Maguire, in her book, and in the film version he seems to be disguised as Player X (Michael Cera), a spiteful creep who wields power for pleasure. If “Molly’s Game” has one unabashed villain, it’s this grinning doofus, who squeezes Bloom out of her own game just because he can. She goes on to even greater fortune in New York, though bigger money turns out to mean bigger dangers.

Sorkin tells Bloom’s story with fast-paced visuals — extreme close-ups, on-screen graphics, rapid-fire montages — and his usual high-word-count writing style that can telegraph information and probe psyches at Intel-chip speed. Chastain, who’s in nearly every frame of the film, delivers an impressively intense, hammered-down performance. In the end, “Molly’s Game” turns out to be a fairly deep-reaching character study of a woman who found her own way of moving through a man’s world.