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: What if the world’s most celebrated mythological beasts—mermaids, minotaurs, and satyrs—were in fact the …