Harriet Tubman, the subject of scholarly works, graphic novels and Hollywood movies, is as well known to grade-school students as she is to viewers of public TV documentaries. In the coming years, as she replaces Andrew Jackson on the $20 bill soon, her image will be carried in millions of American wallets.

What more is there to say about such a familiar historical figure? Plenty, it turns out.

In "Night Flyer: Harriet Tubman and the Faith Dreams of a Free People," her perceptive "faith biography," Tiya Miles focuses on a relatively unsung aspect of Tubman's life — her intertwined relationship with God and nature, which fueled her steadfast moral principles and aligned her with other 19th-century Black women of faith.

In the decade after she fled slavery in 1849, Tubman mounted numerous harrowing rescues, freeing 70 enslaved people. Her heroism continued in the Civil War, when Tubman helped free hundreds of enslaved people during a battle in South Carolina.

Throughout her life, writes Miles, a National Book Award winner (for "All That She Carried") who earned a doctorate in American Studies from the University of Minnesota, "Harriet relied on God first and foremost."

Miles places Tubman in an important Black faith continuum. As Tubman did, Jarena Lee, Zilpha Elaw, Julia A. J. Foote and the writer known as Old Elizabeth wrote and dictated books about their spiritual lives in the decades bracketing the Civil War. These Black women, Miles says, "took radical action to preach and act on what they believed was God's word."

As characterized by Miles, Tubman's faith went through several phases. As a child, she prayed "for a fighting chance in this unjust circumstance." After a head injury suffered when a slave owner threw a heavy object at an enslaved boy but hit Tubman, "she may have passed into a new state of spiritual existence," Miles writes, heightening her faith. She prayed for God to kill the man who enslaved her; she felt remorse when the man died, which "only intensified her religiosity."

Miles cites numerous similarities between Tubman and the other women. All had physical ailments and injuries in their youth, and each viewed these difficulties through spiritual lenses, Miles writes. Likewise, Tubman was among the Black spiritual women of her era who appealed to "God beneath trees, in agricultural fields, and among livestock whom they viewed as sentient."

In some of her dreams, Tubman told a biographer, she flew like a bird above open fields. Elaw and Old Elizabeth used similar imagery to describe themselves. But where their birds were "'speckled,' or darkened by spots," Miles writes, to represent their gender and race — Tubman's seems to have been white, soaring "beyond geographical reality" and unencumbered "by societal rules."

There will always be gaps in Tubman's biography. To Miles, this is no impediment. Tubman bought oxen, Miles writes, but "we can only wonder" if "she whispered to them or stroked their broad flanks before or after a stint of work."

More than many, this book finds beauty in history's unanswerable questions.

Kevin Canfield is a regular contributor to the Star Tribune's books coverage.

Night Flyer: Harriet Tubman and the Faith Dreams of a Free People

By: Tiya Miles.

Publisher: Penguin, 336 pages, $30.