In 1856, a family of slaves attempted to escape their Northern Kentucky masters by crossing the frozen Ohio River. But while waiting in Cincinnati for their guide on the next part of the journey north, they were surrounded by slave catchers. One of the fugitives, a young mother named Margaret Garner, killed one of her own daughters rather than see the child returned to slavery. In a nation already perilously close to civil war over slavery and states' rights, her case caused a sensation, with both abolitionist and pro-slavery orators attempting to use it to justify their own stances. Meanwhile, in Cincinnati courts, the federal fugitive slave law clashed head-on with Ohio's attempt to prosecute Margaret for murder.

More than a century later, Margaret Garner's story became the seed for Toni Morrison's novel Beloved, in which the murdered child haunts her family. After that book became a best-seller, Steven Weisenburger set out to write an essay placing Beloved in its historical context. That essay soon grew to a book: Modern Medea, a detailed and highly readable account of the legal twists and turns and almost unbelievable real-life events in the lives of the Garners that makes the world of slavery horrifyingly real.