What is it about eels? Depending on who you ask, they are a pest, a fascination, a threat, a pot of gold. Eels emerged some 200 million years ago, weathered mass extinctions and continental shifts, and were once among the world's most abundant freshwater fish. But since the 1970s, their numbers have plummeted. Because eels-as unagi-are another thing: delicious.

In Slippery Beast, journalist Ellen Ruppel Shell travels in the world of "eel people," pursuing a fascination with this mysterious creature. Despite centuries of study by thinkers from Aristotle to Leeuwenhoek to Sigmund Freud, much about eels remains unknown. Eels cannot be bred reliably in captivity and infant eels are unbelievably valuable. A pound of the tiny, translucent, bug-eyed "elvers" caught in the fresh waters of Maine can command $3,000 or more on the black market. Illegal trade in eels is an international scandal measured in billions of dollars every year. In Maine, federal investigators have risked their lives to bust poaching rings.

Ruppel Shell follows the elusive eel from Maine to the Sargasso Sea, stalking riversides, fishing holes, laboratories, restaurants, courtrooms, and America's first commercial eel "family farm." This is an enthralling, globe-spanning look at an animal that you may never come to love, but which will never fail to astonish you.