At UC Berkeley, a brilliant research geneticist named Mary-Claire King is embarking on something of a personal crusade to uncover the genetic roots of breast cancer.

She struggles to find a way in the world with her equally young but misguided husband and her older sister, Joan Parker who tries to become a surrogate parent to Anne.

She loses her hair, and if that wasn't enough to endure, her husband, never really mature or stable, has begun an affair with Annie’s closest friend Louise and leaves her.

While she captures headlines for her work applying DNA fingerprinting to help reunite "the disappeared" with their families in Argentina, her priority is to map the breast cancer gene.

King focuses on collecting families with a particularly high incidence of breast cancer, suspecting that these cases are most likely to reveal any genetic predispositions.

Finally, in 1990, King and her team find conclusive evidence linking DNA markers on chromosome 17 with an inherited flaw in a gene dubbed BRCA1.