Cora Fielding dares to dream of becoming a physician, a profession all but closed to women in 1859 America. Her twin brother Carl has already been admitted to California's new medical college even though his true passion lies with his woodcarving skills. Cora, unwilling to bow to the new school's decision not to admit females, disguises herself as a man and gains admittance only to be unmasked by her brother. The resultant furor prompts their physician father to send both to the East Coast, where Cora can follow her dream at the Female College of Philadelphia and Carl can enroll at the University of Pennsylvania's Medical School.
The siblings pursue vastly divergent paths in Philadelphia. Having attained the freedom to choose her own future, Cora finds herself drawn to the plight of those bound in slavery. Her new city being the cradle of the abolitionist movement, she soon becomes embroiled in the activities of the Underground Railroad. Carl, on the other hand, is bored with medicine, a field that holds no interest for him, and he searches elsewhere for gratification. He falls in with like-minded men whose carnal appetites lead them all into a subterranean life of debauchery. Meanwhile, he and Cora are as estranged as they have ever been.
Even as Cora and her new love intervene at their own peril to snatch people from the jaws of slavery, Carl and his friends fall into the much-vilified business of grave robbing. When they run afoul of the law, Cora must make a decision. Allow her brother to fall as a result of his own destructive behavior? Or help him escape his fate and turn back to his art, the one activity that will restore his soul and lead him to the same level of fulfillment she has been able to achieve in her own life? How she decides will determine whether the twins split asunder or go forward in restored, ever-deeper bonds of kinship.