This is a story about a dangerous idea—that all men are created equal—which ignited revolutions in America, France and Haiti; burst across Europe in the revolutions of 1848; and returned to inflame a new generation of intellectuals to lead the abolition movement.Frederick Douglass’s unusual interest in radical German philosophers and Abraham Lincoln’s odd, buried allusions to the same rationalist, secularist, and essentially atheist thinkers are but a few of the clues that underlie this propulsive philosophical detective story.With fresh takes on forgotten thinkers like Theodore Parker (a minister too radical even for the Unitarians, whose work provided some of Lincoln’s most famous lines) and a feisty band of German refugees, Matthew Stewart’s vivid storytelling and piercing insights forge a significant revision in our understanding of the origins and meaning of the struggle over slavery in America—and offer a fresh perspective on struggles between democracy and elite power today.