Margaret Morgan was born in freedom's shadow. Her parents were slaves of John Ashmore, a prosperous Maryland mill owner who freed many of his slaves in the last years of his life. Ashmore never laid claim to Margaret, who eventually married a free black man and moved to Pennsylvania. Then, John Ashmore's widow sent Edward Prigg to Pennsylvania to claim Margaret as a runaway. Prigg seized Margaret and her children--one of them born in Pennsylvania--and...