There is a scene in "The Irishman," director Martin Scorsese's latest and arguably greatest film, where Robert De Niro, playing the real-life mob capo Frank Sheeran, telephones the wife of a man that he has recently killed to commiserate with her.

The bereaved wife doesn't know her husband has died by Sheeran's hypocritical hands.

Onscreen De Niro mumbles a string of incoherent condolences into the phone. He mumbles because the man he killed was actually his closest friend the union leader Jimmy Hoffa, and this murder represents a profound betrayal of every value Sheeran claims to hold.

Read more: All you need to know about Martin Scorsese's "The Irishman"

Sheeran is ashamed of himself in other words, we can see it in his face, but the women on the other end of the line can't. It's an unforgettable moment in a film that's full of them. What kind of man would do such a thing, Scorsese is asking us?

There are no easy answers to be found in this surprisingly funny and increasingly somber film, where behind every big shoot em up moment lies the question of just where is all this headed and what exactly is the point of all this bloodshed and mayhem?

At the start of "The Irishman," it looks like it will be a straightforward crime and punishment drama, but by the middle, it becomes clear that Scorsese is not only telling an organized crime story but also the history of the United States from World War Two to the present moment.

It's a warts-and-all portrait.

You may have heard it's three and a half hours long, but what you won't have heard is that the subject and treatment are so good it could be twice that length and you still wouldn't notice.

The Irishman represents a remarkable return to form for the celebrated director, being the best film he's made in decades and for my money, ever.

You may also have heard that CGI is also used to magically portray De Niro and the cast as their much younger selves. What you may not know yet is that this technology works so well that it doesn't bring the film to an instant standstill, you buy the special effects because the storytelling is already so good.

Based on the bestselling 2004 memoir "I Heard You Paint Houses: Frank The Irishman Sheeran and Closing the Case on Jimmy Hoffa" by former investigator Charles Brandt, the book tells of the improbable real-life rise of the Irish mobster to near the top of the east coast Italian mafia.

Nothing in his life would have predicted Sheeran's criminal career. Born in Darby, Pennsylvania in 1920 he grew up in a small working-class borough on the outskirts of Philadelphia to a family of Irish Catholic descent, about as far from the mean streets as it was possible to be.

By the time he entered World War Two as a US soldier, he had grown to his full adult height of 6 feet 4 inches. Sheeran's war lasted years longer than most other soldiers of his age and in the book, he recalls being called upon by his commanding officers to commit war crimes, including forcing captured German soldiers to dig their own graves then shoot them when they finished.

That kind of callous order, which was also in convention of every conflict standard, resulted in him becoming indifferent to the consequences of killing people, he later confessed. It was also good training for what came later.

We would never have heard of Sheeran if he had not by chance run into crime boss Russell Bufalino at a gas station in the early 1950s. That accidental meeting would change the course of his life, he says.

Bufalino takes a shine to the towering Irishman and soon had him under his employ, setting him up with jobs that get progressively more deadly. Scorsese follows this growing connection between Bufalino and Sheeran like the surrogate father and son relationship it actually was. In a way, it's a love story.

Read more: "The Irishman" hailed by critics as among greatest films ever

What we don't really know is what Bufalino ultimately saw in Sheeran and it's never fully explained in the film either, he simply takes a big shine to the big Irish bruiser and his instinct is rewarded with lifelong loyalty.

But Scorsese has much more in mind than a simple portrait of a mob life or the growing body count. For a start, he has also cast Al Pacino as Jimmy Hoffa, the legendary head of the Teamsters' Union, the charismatic fixer who will eventually become Sheeran's closest friend and eventually, victim.

This development allows Scorsese to show how the mob quickly pilfers union cash to bankroll their own projects, and it also means that their movements come increasingly under the scrutiny of the new Attorney General Robert Kennedy, appointed by his brother, President John F. Kennedy.

Hoffa is particularly incensed by the heat that the Kennedy's have turned up on both the unions and the mob because he says they helped bankroll and support his brother's rise to the White House. It's a betrayal of their investment and their honor, to Hoffa's mind, souring his relationship with the Irish American dynasty in a way that will prove fatal for both of them.

But Scorsese also shows us how the fortunes of the mob mirror that of the nation. Sheeran is shown gun-running (with help from covert CIA operatives) with the mob for an attack on Castro's Cuba.

The mob have an obvious vested interest for signing up to aid an assault on the island, they want to reinstate the casinos for one, but they also want to be rid of the two Irish American brothers that plague them and its heavily implied that the Kennedy assassination is a mob hit, cold payback for turning on them after all the capos have done to get the Irish pair elected.

This is the kind of underworld pulling strings in corridors of power development that makes the film so absorbing. We are far closer to these nefarious hoods than we may be comfortable admitting, "The Irishman" reminds us. Dirty hands are not just something that afflicts small-time criminals and their henchmen.

By implicating some of the most influential people of the 20th century in schemes that are more Godfather than Great Gatsby, Scorsese rubs some of the shine off the Kennedy's in a film that reminds us their initial rise was the result of Prohibition and the sale of illegal booze, facts that brought them much closer to the underworld than Joe Kennedy's offspring were willing to confront or admit, the film suggests.

When we first meet Sheeran in the film he's become an old man who has outlived both the people who supported him and the forces that wanted to bring him down. Near the end of the line, he's finally ready to tell the truth, including that he actually killed his own best friend Jimmy Hoffa, who he realizes at this point no one even remembers.

“In the ’50s, he was like Elvis,” Frank tells his nurse. “In the ’60s he was bigger than the Beatles.” He doesn't ask the next question but we do - so what was the point of his lifelong lust for power and money? What did it do for Frank Sheeran?

Wasting away in a rest home where his estranged daughter refuses to visit, he's a shadow of his former self and yet completely unrepentant for the life that he's lived or the lives he's taken.

Scorsese shows us what Sheeran did and how he did it, but he leaves why he did it up to us, and the lack of easy answers makes this the most mature and unsettling film of his storied career.

Have you seen "The Irishman" yet? What did you think? Let us know in the comments section, below.