The film 12 Years a Slave tells the real-life story of Solomon Northup. In 1841, Northup, a free black man, was drugged and then sold into slavery. How faithfully does the movie capture Northup's life? As part of our week of truth-squadding some of this year's film biopics, Robert Siegel talks with William Andrews, a professor at the University of North Carolina at Chapel Hill. He wrote To Tell a Free Story: The First Century of Afro-American Autobiography, 1760-1865.