Then check out the Salon review of Charles Shields' Mockingbird: A Portrait of Harper Lee.
Margot Mifflin writes:
Though [Mockingbird is] ostensibly about the author, whose Alabama family and Southern racial consciousness inspired "To Kill a Mockingbird," it's also about Lee and Capote, childhood friends who grew up to become symbiotic figures, both personally and artistically, during the '60s. Both were precocious children out of step with their peers, whose slippery grip on gender was a social liability. As Shields puts it, "she was too rough for the girls, and he was too soft for the boys." Each had emotionally absent mothers: Capote's was a self-absorbed social climber; Lee's was chronically depressed, though in her more functional youth she'd played piano at Capote's 16-year-old mother's wedding. (To embroider this family quilt, Capote's father came on to Lee when she was a teenager and she responded by punching him in the nose; Capote hated Lee's gossipy mother, and parodied her, at age 10, in a story called "Mrs. Busybody.")According to this review, a large part of the real value of the biography is the original inquiry into the Lee/Capote relationship.