Philadelphia, the late 1870s. A city of gas lamps, cobblestone streets, and horse-drawn carriages?and home to the controversial surgeon Dr. Spencer Black. The son of a grave robber, young Dr. Black studies at Philadelphia?s esteemed Academy of Medicine where he develops an unconventional hypothesis: that the mythological beasts of legend and lore?including mermaids, minotaurs, and satyrs?were in fact humanity s evolutionary ancestors. And beyond that, he wonders: what if there was a way for humanity to reach the fuller potential these ancestors implied?