"The Invention of Wings," by Sue Monk Kidd Unlikely alliances are a staple of fiction, and the unlikelier the better, from Huck and Jim floating down the Mississippi to Frodo and Gollum creeping toward Mordor - because the real drama lies in watching how dissimilar characters turn out to be brothers (or sisters) under the skin. Sue Monk Kidd followed this principle in her best-selling first novel, "The Secret Life of Bees," in which a 14-year-old white girl and her family's black servant join in fleeing abuse in the South Carolina of the civil rights era. Kidd's latest novel, "The Invention of Wings," also set largely in South Carolina, involves another unusual duo, in this case a slave and a daughter of the family that owns her. The story begins in Charleston in 1803 on the day 11-year-old Sarah Grimké is given Hetty, or "Handful," roughly her same age, as a birthday present. A born abolitionist whose earliest memory is of witnessing a slave being whipped (a trauma that's responsible for the stammer that still afflicts her), Sarah immediately tries to "return" Handful. When this attempt fails, she writes an official "certificate of manumission," which is promptly torn in two. Although Handful has to serve as Sarah's personal maidservant, the girls share confidences and even an illicit picnic on the roof. Sarah also teaches Handful to read and write, an infraction that results in harsh penalties for both. Zosia Dzierzawska To her credit, Kidd doesn't insist on a close friendship between these characters. They like each other, but uneasily, Sarah out of guilt and Handful because she knows she's listed on a household inventory "right after the water trough, the wheelbarrow, the claw hammer and the bushel of flint corn." Instead, through alternating chapters narrated by Sarah and Handful, spanning 35 years, the novel juxtaposes their experiences of oppression. Plain but studious Sarah reads Voltaire, studies Latin with an older brother and dreams of becoming the first female jurist. But when she reveals this ambition to her father, a judge, he declares angrily that she's speaking "nonsense." Her mother later tells her that "every girl must have ambition knocked out of her for her own good" and forces her to start husband-hunting. Meanwhile, Handful's mother, Charlotte, a rebellious and talented seamstress, makes a "story quilt" detailing the history of their bondage, beginning with the kidnapping of Handful's "granny-mauma" in Africa. Early on, Charlotte is also hideously punished for stealing a bolt of cloth. Naturally, Handful distrusts all white people, even the painfully well-meaning Sarah, and soon turns rebellious herself. The truly harrowing moments in the book all belong to her and, inevitably, so does the larger share of the reader's sympathy. Yet, as the novel's title suggests, the desire for freedom inspires both heroines to defy their restrictions - one overtly, the other covertly. The first scene opens with Charlotte telling Handful that long ago "in Africa the people could fly." She then pats the child's shoulder blades, assuring her: "This all what left of your wings. They nothing but these flat bones now, but one day you gon get "em back." That Handful and Sarah both take flight by the end of the novel is not perhaps very surprising. What might be surprising, for some readers, is to learn that Sarah Grimké is a historical figure, an energetic abolitionist from a slaveholding Charleston family. After moving to Philadelphia and becoming a Quaker, she began speaking publicly against slavery and crusading for women's rights. With her sister, Angelina, and Angelina's husband, Theodore Weld, she wrote "American Slavery as It Is," a "testimony of a thousand witnesses" that influenced Harriet Beecher Stowe's novel "Uncle Tom's Cabin," published 13 years later. Although notorious in their own time ("arguably the most famous," according to Kidd, "as well as the most infamous women in America"), the Grimké sisters are less well known today. Kidd's intention, as she explains in an author's note, was to write not a "thinly fictionalized account" of Sarah Grimké"s life, but rather a "thickly imagined story" based on extensive biographical material, including diaries, letters and newspaper accounts. Handful, however, is almost wholly imagined. A slave named Hetty was indeed presented to Sarah Grimké, but the actual Hetty died in childhood and nothing more is known about her. It's curious, therefore, that of the two narrators, Handful is the more believable. She certainly has the more vivid voice. "The smells in there would knock you down," she notes of the stalls at the Charleston market, and after a frightening moment reveals "my heart had been beat to butter." By contrast, Sarah is given to weighty pronouncements: "For all my resistance about slavery, I breathed that foul air, too." Both Handful and Sarah are admirable characters, though rather disappointingly so. Improbable allies are most engaging when they make life hard for each other and generally it takes them a while to find their common pulse. But Sarah empathizes so completely with Handful from the very beginning that we never get to doubt their innate sisterhood. While their identities as mistress and slave imply conflict, it's not a conflict played out between them. Handful's rich resentment is rarely directed at Sarah. How could it be? The actual Sarah Grimké may have been as earnest and honorable as she is here, but a little less righteousness might have furnished this story with a wider wingspan. By Sue Monk Kidd