Atlanta author Denene Millner was 12 years old and snooping through her parents’ things one day when she came across a document that revealed a big family secret: She was adopted. Raised in a sheltered household by strict but loving parents who taught her to be obedient and not rock the boat, she kept her discovery secret until after her mother’s death many years later.

But the impact of being adopted and the questions it raised about her origins started to loom large in her mind as she got older and became a mother to two daughters of her own. As she began to do some research, she came to realize the story she’d been told about being left on a stoop as an infant was a gross oversimplification of what really transpired. Eventually she was consumed with learning more and filling in the blanks with her imagination, the result of which is the New York Times bestselling author’s most ambitious and most personal novel yet, “One Blood” (Tor/Forge, $29.99), which publishes Sept. 5.

Spanning from 1965-2004, “One Blood” is separated into three sections, each one focused on one woman’s life: Grace, an unwed mother forced to surrender her newborn daughter; Lolo, the adoptive mother who’s shamed by her inability to birth a child; and Rae, their daughter, now an adult, pregnant with a daughter of her own.

Millner, 54, is a masterful storyteller, but “One Blood” is so much more than a good yarn. This thought-provoking book explores a lot of important issues: forced adoption, generational trauma, toxic parenting, racial prejudice, classism within the Black community, changing gender roles, the sexualization of Black women’s bodies. The one overarching theme, though, is what exactly defines a family.

A one-woman publishing powerhouse, Millner has cowritten dozens of adult books over the years including romance novels, relationship advice books and celebrity memoirs. TV host Steve Harvey, actress Taraji P. Henson, opera singer Jessye Norman, singer Charlie Wilson and reality show star NeNe Leakes are among her collaborators. She’s also written several children’s books and has her own imprint with Simon and Schuster focusing on books that, according to her website, “speak to the human experience of African American children, beyond the typical subjects saddled on them, like the civil rights movement, slavery and the lives of sports and music icons.” She’s also co-host of the nationally syndicated PBS show “A Seat at the Table.”

Despite all those many accomplishments, Millner says “One Blood” feels like her first book.

“This is my first adult novel that I’m writing on my own wholly from my imagination. And it’s based off of questions I had about my own life, my mom’s life and my birth mother’s life, and what that all meant for each of us as women, especially Black women in America,” she said speaking from her father’s home in Virginia. “This book is deeply personal for those reasons.”

The story she told herself after learning about her adoption was that her birth mother had not abandoned Millner because she was unwanted, but she was regretfully surrendered to a loving family out of necessity. She refused to attach anything nefarious to her origin story.

But late one night while working on the book, she was running some Google searches when she discovered the “hospital” where she was born was actually a home for unwed mothers. Not only that, it was notorious for “ripping children away from mothers and giving them to couples that were married and acceptable to society and who needed to be a part of this 2.5 kids, white picket fence, two-parent household,” she said.

“It just hit me at 2 o’clock in the morning that I was most likely taken from my mother … and it tore me to shreds to have that information and know what most likely happened. … That’s when I started to think more deeply about how adoption actually affected me and to dig deep into how I relate to other people, how I relate to my family and how my personality kind of falls in line with a child of adoption, constantly trying to connect with people and hoping it sticks because I may have abandonment issues. That was a revelation that night.”

All of that personal insight beautifully informs “One Blood,” which is based on fact but also contains a whole lot of fiction.

But here’s a startling truth about Millner’s life that proves once again fact is stranger than fiction every time.

First some backstory: Millner was born in New York, grew up in New Jersey and moved to Snellville in 2005 with her then husband and their two children. A few years ago, she decided to try to track down her birth mother. She was surprisingly easy to find. Unfortunately, she had died in 2017, but guess where she lived. Yep. Snellville.

“I just feel like when you are a mother and you have a baby that there is an inseparable bond there,” Millner said, her voice growing thick with emotion. “There is no way you can separate yourself from one another. … I feel like somehow our cells were insistent on being with each one other in some kind of way. That’s the only way I can describe how we would both end up in random ass Snellville, Georgia, at the same time.

“I really do believe the universe and the blood leads us to one another.”

Charis Books & More presents Millner in conversation with author Tayari Jones at 7 p.m. Tuesday, Sept. 5, at the Auburn Avenue Research Library. charisbooksandmore.com. The event will be simulcast online at www.facebook.com/AuburnAvenueResearchLibrary.

Suzanne Van Atten is a book critic and contributing editor to The Atlanta Journal-Constitution.