“The Irishman,” fabled director Martin Scorsese’s new three-and-a-half-hour Mafia saga, debuts in select cinemas on Friday before dropping on Netflix on Nov. 27, just in time for Thanksgiving binge-watching. The dense, sprawling, surprisingly melancholic drama revolves around Frank Sheeran (Robert De Niro), a self-proclaimed hitman who said he gunned down Teamsters boss Jimmy Hoffa (Al Pacino) in 1975.

The film has stoked anticipation rare for a Hollywood production without a Marvel character or “Star Wars” in the title, and it’s not hard to understand why. It marks Scorsese’s triumphant return to the mob genre for the first time since his Oscar-winning “The Departed”; a rare reunion for co-stars De Niro and Pacino; a big-screen comeback for supporting player Joe Pesci; and a $159 million gamble by its Oscar-hungry distributor, Netflix.

If you’ve haven’t kept tabs on the Film Twitter hype and industry chatter, here’s a primer on some of the key questions and storylines swirling around “The Irishman.” (No major spoilers here, so you can breathe easy.)

“The Irishman” is largely adapted from “I Heard You Paint Houses,” a 2004 book by former homicide prosecutor Charles Brandt that chronicles the life of Sheeran, an International Brotherhood of Teamsters official who said he worked as a contract killer for the Bufalino crime family in the Philadelphia area. Sheeran, who died in 2003, cast himself as the Forrest Gump of the 1970s Northeastern crime circuit, purportedly responsible for the killings of Hoffa, New York gangster Joseph “Crazy Joe” Gallo and other underworld tough guys. Hoffa’s unsolved death, most notably, has vexed true-crime aficionados for decades.

Scorsese and De Niro, who read Brandt’s book and have worked to get a film adaptation off the ground for more than 15 years, present Sheeran’s version of 20th century history, depicting the stoic World War II veteran as having carried out a series of slayings from the 1950s through the early 1980s. The film, principally told in slow-burning flashbacks and punctuated by mournful voice-over by De Niro, even winks at the possibility that Mafia figures were tied to the assassination of President John F. Kennedy in 1963.

But historians, academics and amateur sleuths have long cast doubt on Sheeran’s claims as relayed in Brandt’s book, with some unequivocally stating that the labor union official was nothing more than a fabulist. Two recent, copiously detailed articles tied to the release of “The Irishman” — journalist Bill Tonelli’s “The Lies of the Irishman” in Slate and Harvard Law School professor Jack Goldsmith’s “A True Crime Story?” in the New York Review of Books — are required reading for viewers curious about rebuttals to Sheeran’s side of the story.

“The Irishman,” among other achievements, is responsible for a handful of long-awaited reunions and at least one first-time collaboration.

Scorsese and De Niro add another chapter to one of the most fruitful partnerships in American film history, teaming up on a feature-length project for the ninth time. Pesci, who won an Oscar for his bravura performance in “Goodfellas,” came out of unofficial retirement to work with Scorsese for the fourth time. Pacino, for his part, had never acted in a Scorsese film before, although he co-starred with De Niro in the 1995 crime classic “Heat” and the 2008 buddy cop thriller “Righteous Kill,” a critically reviled production that neither actor, as they recently told NBC News’s Harry Smith, remembers fondly.

But when crime connoisseurs head to the multiplex (or their living room couch) for “The Irishman,” some might be surprised by the relative lack of wrinkles on these familiar faces. Scorsese and his production crew hired Industrial Light & Magic, a visual effects firm founded by “Star Wars” creator George Lucas, and the Oscar-nominated effects wizard Pablo Helman (“War of the World”) to give the main cast a computer-generated facelift with a technique known as “de-aging.” The video below explains the nitty-gritty:

The process, met with equal parts enthusiasm and consternation in the film industry, has been put to use in at least six Marvel franchise entries — Samuel L. Jackson was “de-aged” some 25 years for “Captain Marvel,” for example — and most recently in the Will Smith action vehicle “Gemini Man.” But the visual effects in “The Irishman” could mark a turning point, previewing a future where “de-aging” technology is common not just in summer blockbusters but also in somber dramas with more lofty artistic ambitions and decade-spanning timelines.

“The Irishman” was originally set up at Paramount Pictures, the studio that has released most of Scorsese’s features from the last decade, including “The Wolf of Wall Street” and “Silence.” But as the budget ballooned, partly due to the mounting cost of the “de-aging” technology, Paramount effectively dropped the project — and that’s when streaming giant Netflix swooped in and purchased the movie for more than $100 million.

In recent years, Netflix has courted A-list directors with promises of creative freedom and a global distribution platform, wooing top-tier talents such as the Coen brothers (“The Ballad of Buster Scruggs”), Korean auteur Bong Joon-ho (“Okja”) and Steven Soderbergh (“The Laundromat”), among others. Scorsese, widely considered the greatest living English-language filmmaker, is indisputably a giant feather in Netflix’s cap.

Netflix is clearly gunning for the critical respect and marketing prestige that traditionally leads to glory at the Academy Awards, where last year the company scooped up honors for Alfonso Cuarón’s “Roma” but fell short of the best picture trophy. “The Irishman,” joined on Netflix’s fall slate by Noah Baumbach’s “Marriage Story” and Fernando Meirelles’ “The Two Popes,” gives the company another shot at racking up awards it can then dangle in front of potential subscribers.

The glowing reviews “The Irishman” received after it premiered at the 57th New York Film Festival in September signal the film could charge into awards season as a major contender, even as the country’s largest theater chains — AMC, Cinemark, Regal — have refused to screen it. The reason: Netflix, as it did with “Roma,” wants to make it available to stream after only about a month on the big screen, shrinking the roughly three-month theatrical “window” and depriving exhibitors of additional revenue.

New Yorkers, however, will have a chance to avoid conventional movie theaters altogether. Netflix has arranged for “The Irishman” to play at the Belasco Theatre, a Broadway institution that in its 112-year history has never screened a film. But the venue has been outfitted with state-of-the-art equipment for the monthlong run.