In cinephile shorthand, “The First Omen” comes off as an homage to the gory cinema of Dario Argento as imagined by someone who’s only heard descriptions of the famous/infamous Caravaggio of motion picture horror.

For a cynical, “Let’s milk this intellectual property for all its worth” exercise, this fifth film in the “Omen” franchise is self-consciously artistic, gruesomely grisly, and almost wrestling with big issues — abortion, the collapse of Catholicism and a plot to “bring people back to the Church” by scaring them via the Antichrist.

And it’s built around a riveting performance by”Game of Thrones” alumna Nell Tiger Free, as a nun new to a Roman orphanage and hospital where Satan’s spawn might be born.

The film is a prequel to the iconic 1976 Gregory Peck/Lee Remick thriller about a couple raising a little boy named Damien, whom they don’t realize is the Antichrist.

Set in 1971, this “”First Omen” meanders between the cheap-jolts filmmaker Arhasha Stevenson must have been contractually-obligated to provide. The plot is Byzantine, but can’t avoid predictable tropes and situations and “twists” of the genre.

Yet with Bill Nighy as an Archbishop, Charles Dance and Ralph Ineson as priests on opposite “sides” of whatever is going on, with Sonia Braga as a stern and sary nun in charge of the orphanage, you can’t write the film’s ambitions off.

An investigating priest (Ineson) finds his way to an aged cleric (Dance) with the message, “Hiding won’t absolve your sins.” The old priest was mixed-up in a conspiracy that the younger one is trying to unravel.

In Rome, the once-orphaned American Margaret (Free) has arrived to the warm embrace of the Archbishop (Nighy) who sponsored her to be a novitiate at the convent that runs Roman Catholic orphanage and hospital.

She is “taking the veil” in 1971 Rome, where unrest has workers on the streets, as it was in many European capitals. Youth are protesting the Vietnam War and out-of-touch governments everywhere. People “are turning away from the church in droves,” in part because of its ancient rituals, but also thanks to its historical/institutional connection to money, power, dictatorships and authoritarian politics.

And weird things are going on in that hospital. A disturbed teen who draws nightmarish visions of how she sees the world is kept isolated from the others. Treatments and punishments are done behind closed doors.

When now-defrocked Father Brennan (Ineson) gets Margaret’s attention, he tries to enlist her help in finding “proof” of his suspicions, that the Church is manufacturing a crisis to save itself from an indifferent world.

Director Stevenson, tapped to make his feature filmmaking debut with an episode of TV’s “Legion” his most significant credit, treats us to faintly-chilling settings, to shadows and extreme closeups, and a riveting meltdown turn by Free, as Margaret cannot believe what she’s discovering and lives in terror at what her role in it all might be.

The few effects are grisly and old-school shocking, and the period detail — novice nuns enjoying a bit of Roman nightclubbing before they “hide this body (theirs) forever,” getting caught up in marches and riots — is spot on.

But this “Omen” lurches between “dull” and “soul-sucking boredom” more often than any edit or re-edit could fix. The tedium sets in as the pacing slacks, and as the pacing slackens off the stakes are lowered.

There’s little of the “Future of Humanity” urgency of the 1976 Richard Donner film, released after “The Exorcist” and “Rosemary’s Baby” got an increasingly secular world all worked-up over the Devil and what he might do to get our attention.

This script gets so wrapped up in the back-engineering of the story, the nuts and bolts of “There is a beast they’re making,” that it loses track of just how shocking that might have seemed, then and now.

And the shocks themselves are less shocking than you’d hope, and far too few in number.

But to her credit, the cast, especially Nell Tiger Free, never lets on that the terror isn’t real. She never loses her commitment to the character’s reality, even when the picture is serving up the trite, tried and true pro forma epilogue of many an “historic” horror saga.

If only the film around these players had been more worthy of their efforts.

Rating: R, violent content, grisly/disturbing images, and brief graphic nudity.

Cast: Nell Tiger Free, Ralph Ineson, Sonia Braga, Maria Caballero, Charles Dance and Bill Nighy.

Credits: Directed by Arkasha Stevenson, scripted by Tim Smith, Arkasha Stevenson and Keith Thomas. A 20th Century release.

Running time: 2:00