Almost irresistibly old-fashioned, Miss Sloane revolves around a magnetic performance by Jessica Chastain.

She portrays the titular character, Elizabeth Sloane, a lobbyist known far and wide in government circles for doing whatever it takes to score a win for her client. She is not known for her ethics, personal or otherwise, and her employers at a large Washington firm only care about the results. Nonetheless, something within her is stirred when she is faced with a new client who wants to defeat an upcoming bill that would impose additional gun control restrictions.

Her feisty response gets her in hot water with her boss, George Dupont (Sam Waterston) and leaves her open to an offer from a boutique lobbying firm run by Rodolfo Schmidt (Mark Strong). She quits the big firm, taking most of her team with her, except for the resentful Jane Molloy (Alison Pill), and brings her aggressive tactics along too for an epic battle with entrenched politicians and the forces of evil.

At the small firm, she meets Esme Manucharian (Gugu Mbatha-Raw), who has been doggedly fighting gun laws for eight years. Elizabeth immediately sizes her up as a perfect spokesperson for her new campaign. As Esme reluctantly appears on TV shows and sits down for interviews, Elizabeth wages war behind the scenes, engaging with her former colleagues, led by Pat Connors (Michael Stuhlbarg), as both sides seek to secure U.S. Senators to vote in their favor on the bill.

What soon becomes apparent is that the first produced original script by Jonathan Perera is a sure-fire crowd-pleaser — as long as the crowd is firmly in favor of gun control! — and is thus reliant on creaky mechanics, hissable villains, and heroic supporting characters with unshakable integrity and devotion to righteous causes.

Elizabeth Sloane is the apparent exception, in that her ethics are in question from the start, especially since the movie begins with her appearance before a congressional committee led by the righteous Congressman Sperling (John Lithgow). Elizabeth is in serious hot water, and the film then rewinds to show how she got to that point.

As the story develops, however, it also becomes clear that Elizabeth is whip-smart, and that she is more than capable of taking care of herself and those who are loyal to her. She is also very clever about setting things up; to say more would spoil some of the many twists that play out in a manner that is satisfying, if a bit predictable once the mouse traps start clamping shut.

Chastain is a veritable force of nature, fully in command of her character and the movie. She’s such a magnetic presence in the role of Elizabeth Sloane that she draws constant favorable attention, even when she’s doing things that appear to be morally questionable and legally actionable, such as when she meets her weekly “date” (Jake Lacy) to work out her focused sexual energy.

With all its predictable turns, Miss Sloane is still more entertaining than it should be, largely because of Chastain’s charm and drive, bolstered by a very strong cast that plays to their individual strengths. Miss Sloane may be a liberal fantasy, but it’s quite a boisterous and enjoyable show.

The film opens today in theaters throughout Dallas.