The keenly focused intelligence and low-boil intensity that James Vanderbilt demonstrated in his screenplay for “Zodiac” are on impressive display in “Truth,” a portentously titled but duly absorbing, blow-by-blow account of the “Memogate” controversy that shamed CBS News, ended Dan Rather’s career as the network’s anchorman, and became a chastening historical footnote to the re-election of President George W. Bush. As Vanderbilt’s crisp, polished directorial debut takes pains to remind us, it also led to the downfall of “60 Minutes” producer Mary Mapes, cast here as the fierce, embattled heroine of a stomach-knotting newsroom thriller that plays like both a companion piece and a counterpoint to the more edifying “Spotlight”: It’s the feel-bad journalism movie of the year, a despairing last gasp for an era when substance mattered more than scandal. Complex, incisive and high-minded, sometimes to a fault, the Oct. 16 Sony Classics release should spin its juicy subject matter and lead turns by Cate Blanchett and Robert Redford into a solid commercial showing during another noisy election season; still, there remains a somewhat too-tidy fastidiousness to the picture that will keep it securely in the “pretty good” tier of 2015 prestige releases.

Introduced hiring a lawyer who will represent her during an internal investigation that CBS is conducting, Mapes initially comes across as a figure only moderately less wired and desperate than the Xanax-popping socialite Blanchett played in “Blue Jasmine.” It’s a slightly unflattering introduction in a picture that is otherwise fairly transparent about mounting a cinematic vindication of sorts for Mapes, whose 2005 book, “Truth and Duty: The Press, the President, and the Privilege of Power,” provided the foundation for Vanderbilt’s screenplay. In short order, the film flashes back to April 2004, with the producer in her “60 Minutes” prime — a widely respected and accomplished figure in her field whose long-running collaboration with Rather (Redford) has just enjoyed a career peak with their groundbreaking report on Abu Ghraib. As Mapes herself notes with more objectivity than ego, their work is “the gold standard,” a bastion of investigative rigor in an industry that devotes less and less time and resources to serious news gathering.

Which is not to say that Mapes doesn’t enjoy sinking her teeth into the latest “juicy piece of brisket” that’s landed in her inbox, a tip concerning alleged links between Bush and the bin Laden family. The lead goes nowhere, but at a key moment in the presidential campaign, with the swiftboating of John Kerry under way, it does trigger a productive inquiry into Bush’s own military record — specifically, the suspicion that he used his family connections to dodge Vietnam and land a coveted spot in the Texas Air National Guard in 1968, a favor courtesy of the state’s then-lieutenant governor, Ben Barnes (Philip Quast). But the evasions may have gone even deeper, on the evidence of six documents that have recently come to light, and which appear to have been written in 1972-73 by Bush’s commander, the late Lt. Col. Jerry B. Killian; collectively, they make the damning claim that Bush’s service was spotty to nonexistent, as he never showed up for his physical or fulfilled any of his obligations as an officer.

Determined to break the story early, not only to beat the competition but also to avoid any sense of an “October surprise,” Mapes assembles a sterling team of investigators and researchers, who are swiftly introduced with heist-crew flair: freelancer Mike Smith (Topher Grace), who’s been following the Bush/National Guard story for some time; Lt. Col. Roger Charles (Dennis Quaid), a Vietnam vet serving as a consultant; and journalism professor Lucy Scott (Elisabeth Moss). Vanderbilt’s multilayered script settles easily into the even-keeled procedural style of “Zodiac” as the team sets out to authenticate the documents, calling in different experts to study Killian’s signature and (crucially) the text of the memos, which would have to have been produced on a ’70s-era mechanical typewriter.

Even as it clues us in to potential oversights and missteps, “Truth” paints its fact finders in the most scrupulous light possible: They’re well aware that the outcome of their reporting could influence the election (with Kerry leading the polls by a slim margin), and therefore that much more intent on ensuring that their story is airtight. And it seems to be, especially after Mapes scores an over-the-phone confirmation of the documents’ veracity from Killian’s superior, in a scene that Vanderbilt shoots in a riveting single take, the camera locking Mapes in its sights while she pins down her source. Rather delivers the story with his usual stentorian authority, and Mapes and her team enjoy a fleeting sense of accomplishment — before the story is picked up and immediately challenged by conservative bloggers and, more importantly, other major news outlets, who quickly latch on to the suspicion that something major has slipped through the cracks.

If the film’s emotional temperature inevitably rises several degrees in the second act, editor Richard Francis-Bruce maintains an unwavering, locked-down focus, even as Mapes and her team are slowly raked over the coals. First come alarming charges that the memos could easily have been fabricated on a computer; then the inevitable loss of confidence from their CBS News higher-ups Andrew Heyward (Bruce Greenwood) and Betsy West (Rachael Blake); and finally, a startling admission that, had it come to light earlier, would surely have kept the story off the air. But what this thoughtful, slippery film leaves us to consider is that the unraveling of one chain of evidence hardly amounts to a refutation of the larger story, which was promptly buried in an avalanche of public disgrace — some of it piled on by a network that realized it might be in its best corporate interests (and those of its parent company, Viacom) to play nice with the incumbent and future administration.

Given that it’s become a popular awards-season bloodsport to challenge prestige docudramas and biopics on factual grounds, a movie called “Truth,” implicitly defending a group of journalists who were accused of falling short of that standard, would seem to be marching into the fray with a giant “Debunk Me” sign on its back. It’s a credit to Vanderbilt that despite his measured and exacting tone, he never lapses into a posture of objectivity: His movie surveys Bush’s legacy with withering restraint, openly mourns missed opportunities to derail his presidency, and is at times overly fond of stuffing its own opinions into its characters’ mouths — as when Grace’s Smith lets loose a stream of invective against “60 Minutes II” exec producer Josh Howard (David Lyons) for so readily hanging his employees out to dry.

And in the end, to a degree that will strike detractors as excessively soft and sympathetic, “Truth” is clearly and unapologetically on Mary Mapes’ side. Really, given the movie’s choice of leading lady, it could scarcely be otherwise. Suffering only from a measure of familiarity when set beside the actress’s other work, Blanchett’s performance is forceful yet delicately shaded, and she renders Mapes with admirable complexity: We see a hard-working wife and mother who struggles to find time with her supportive husband (John Benjamin Hickey) and young son, but also a tough-as-nails producer whose excitement outstripped her attention to detail at one crucial moment. She is, too, a successful career woman frequently accused of harboring a radical feminist agenda and/or allowing her liberal politics (which is to say, her emotions) to interfere with her professional distance — a charge that Vanderbilt allows Mapes to answer with blistering eloquence in one of his most pointedly written and directed scenes.

The film also gives us a few dribbles of emotional backstory regarding Mapes’ difficult relationship with her cruelly abusive father, which played a formative role in her professional development (“I don’t like bullies”) and also led her to form a sort of surrogate daughter-father bond with Rather. Redford, who bears a solid resemblance to Rather but not quite enough to make you forget whom you’re watching, plays the veteran newsman with easy gravitas, inner strength and a gentle paternal twinkle, with little display of the anger and volatility for which he was often known over the course of his storied career. More than a decade after leaving CBS News, Rather gets a touching, valedictory sendoff here, in a sequence that reveals the film’s intentions a bit too baldly while overdosing on Brian Tyler’s otherwise pulsingly effective score.

Vanderbilt’s filmmaking is as clean and unshowy as his scripting, and he demonstrates superb instincts with actors; notwithstanding the sometimes-distracting starriness of his two leads, “Truth” is more than a match for “Spotlight” in showcasing an ensemble that feels impeccably cast down to the smallest role. Grace and Quaid relax nicely into a more collegial rapport than they shared in “In Good Company” (2004); Moss makes the most of her too-few scenes as an intrepid reporter thrilled to be on the case, and Greenwood, Lyons and Blake all strike sharp, memorable notes as CBS heavyweights forced into damage-control mode. Stacy Keach is at once pitiable and exasperating as Lt. Col. Bill Burkett, the National Guard veteran who furnishes the faulty smoking gun, and as his wife, Noni Hazlehurst has one blazing, Beatrice-Straight-in-“Network”-caliber scene in which she takes Mapes and her team to task for trying to shift the blame. “You don’t care,” she lashes out, even if this skilled and compelling dramatization makes clear that the truth of the matter is, as always, more complicated than it appears.