True-crime thrillers rarely hit as hard and with such redeeming spirit and soul as "Under the Banner of Heaven," a seven-part FX on Hulu streaming series that stars a superb Andrew Garfield as a Mormon detective investigating the 1984 Utah murder of a mother and her 15-month-old daughter that involves a secret fundamentalist sect within the church.

Adapted by Dustin Lance Black, an Oscar winner for "Milk," from the 2013 bestseller by Jon Krakauer, the series begins at the murder scene (not graphically shown) as senior officer Jeb Pyre (Garfield) launches an investigation that will lead him to question his own beliefs.

PHOTO: Gil Birmingham and Andrew Garfield in "Under the Banner of Heaven," 2022.
FX Networks
Gil Birmingham and Andrew Garfield in "Under the Banner of Heaven," 2022.

The Mormon-raised Black served as a writer on "Big Love," the HBO series about a polygamous Mormon family. He uses Jeb -- a fictional character not in the Krakauer book -- as an audience guide into the double murder and the origins of The Church of Jesus Christ of Latter-day Saints as set down in 1830 by founder Joseph Smith and his successor Brigham Young.

Don't expect a dull history lesson or a biting satire on the order of the Broadway musical smash "The Book of Mormon." It's "blind" faith that Black and director David Mackenzie ("Hell or High Water"), who staged the first two episodes, have in their sights.

Through Jeb, a devout family man and father of two, we see a true believer whose convictions are shaken by dangerously authoritarian splinter groups within the church. Garfield is on a career roll ("Tick, Tick ... Boom," "Spider-Man: No Way Home," a Tony Award for "Angels in America") and his nuanced portrayal of Jeb places him among the best actors of his generation.

Jeb's chief suspect is Allen Lafferty (a strong, stinging Billy Howle), the husband of the slain Brenda Lafferty, a progressive Mormon played by Daisy Edgar-Jones ("Normal People") with such heat and heart that we root passionately for Jeb to find her killer.

It's always the husband, says Jeb's non-Mormon partner Bill Taba (the excellent Gil Birmingham) who cringes each time Jeb refers to Allen and other fellow Mormons as "brother" or "sister." He has a point.

PHOTO: Andrew Garfield in "Under the Banner of Heaven," 2022.
FX Networks
Andrew Garfield in "Under the Banner of Heaven," 2022.

Suspicion soon extends past Allen to the entire Lafferty family, so revered in the community that they're called "the Utah Kennedys." Dissension within the ranks is palpable when the family patriarch passes over his eldest son Ron (Sam Worthington) to place leadership duties on Dan (Wyatt Russell, blending charm and menace with spellbinding skill).

"Under the Banner of Heaven" builds to a crescendo of suspense. But the whodunit aspect of the series is secondary to the way it tries to separate faith from fanaticism. Is there anything OK about a Mormon father having sex with his two stepdaughters, ages 12 and 14, as a tenet of faith to save a once-persecuted religion from extinction?

"Our faith breeds dangerous men," Jeb is told. And that loaded statement electrifies every scene in this series that uses the past to ask pertinent and unsettling questions about the rise of fundamentalism in a modern world where women need to be subjugated to their masters and "blood-atoned" for the sin of disobedience.

The uses and abuses of faith permeate this hypnotic and haunting series. Believe this: "Under the Banner of Heaven" is a dramatic powerhouse that will take a piece out of you.