Movie critic

From left, Bryan Cranston, Laurence Fishburne and Steve Carell as Sal, Mueller and Doc, three Vietnam War buddies who abruptly reunite in 2003 as the result of a different war: Iraq. (Wilson Webb/Lionsgate)

An ambling, low-key vibe pervades “Last Flag Flying,” which has been billed as a spiritual sequel to Hal Ashby’s 1973 “The Last Detail” and lives up to that promise. As the film opens, the meek, mustached Larry “Doc” Shepherd (Steve Carell) pays a visit to a Norfolk bar run by Sal Nealon (Bryan Cranston), quietly nursing his beer until Sal recognizes who it is: The two served in Vietnam together 30 years earlier, when Larry was sent to the brig after an unnamed infraction that they refer to with knowing looks and half-sentences.

It turns out that Larry, who has been living in Portsmouth, N.H., is on a mission, for which he wants to enlist Sal and another war buddy, Richard “The Mauler” Mueller (Laurence Fishburne), now a pastor living outside Richmond. Once underway on their journey, the three present a grizzled, slightly wan semblance of the characters Jack Nicholson and Otis Young brought to life three decades ago in a similarly eventful journey.

Although they’re clearly different, Doc, Sal and Mueller share some brushstrokes with the characters from Ashby’s film, who were on their way to deposit a miscreant (played by a young Randy Quaid) to a Portsmouth military facility. “Last Flag Flying,” which takes place in 2003, obliquely revisits the events that put Doc in detention, but the main focus of the film is the Iraq War, one of whose casualties he and his friends are now in charge of seeing to his final resting place.

As a picaresque that takes its protagonists from the Virginia Tidewater to New England, “Last Flag Flying” has an episodic structure that feels dangerously close to schematic, plunking these middle-aged men in the middle of high jinks that include a misbegotten attempt to rent a truck while invoking Osama bin Laden, and, later, the acquisition of newfangled devices called cellphones. Thankfully, director Richard Linklater and co-writer Darryl Ponicsan, who wrote the 2005 book on which the film is based, mellows out the piece’s inherent staginess, infusing a mournful but often observantly funny story with his distinctive unobtrusive, slightly ruminative style. (The film is a production of Amazon Studios; Amazon founder and CEO Jeffrey P. Bezos owns The Washington Post.)

Of course, “Last Flag Flying” lives or dies by the chemistry generated by its stars. Here, three fine actors play off one another with gentle deference and affection that seems genuine and unforced. Carell isn’t always entirely believable as a Vietnam veteran — even one who signed up as a teenager — but over time, his character takes on gravitas that winds up being deeply moving. As the group’s self-appointed moral conscience, Fishburne never makes Mueller a prig, but simply a man of spiritual discipline that’s put to the test every moment that he’s forced to remember events he’s spent 30 years trying to atone for.

His biggest challenge in that regard is the hard-drinking, foul-mouthed Sal, played by Cranston with the glee of a man who knows the precise worth of the comic relief he’s providing. Together, the ensemble achieves an improbable feat, bringing to life not only the men their characters are during the film’s time period, but also, at times, the far different people they were during the war. Unsurprisingly, “Last Flag Flying” engages with such timeless issues as honor, loyalty, the fecklessness of top brass and the futility of war. By the time the threesome pulls into their final stop, those bullet points have been replaced with real feeling, brought to a particularly moving climax in the film’s quietly shattering penultimate scene. For its studiously modest, unassuming tone, “Last Flag Flying” is a movie of enormous humanity and heart.

R. At area theaters. Contains crude language throughout, including sexual references. 124 minutes.