The main theme of the book has to do with the nature of obsession and how a passion for something can turn into obsession. The main character, John Laroche, personifies this phenomenon. His obsession borders on being a compulsion; he does not seem able to function without channeling his passions into something all-consuming.

Orlean describes how, over the course of many years, Laroche flitted from passion to passion: tropical fish, photography, orchids, fossils, and others. He first fixated on turtles as a child. Orlean describes it developing from a normal fascination with turtles to a state in which “life wasn’t worth living unless he could collect one of every single turtle species” (4). For Laroche, the obsession itself became foremost rather than the object of his passion, as he would quit one interest abruptly and have nothing more to do with it—moving on completely to a new collecting interest.

The book focuses on an obsession with orchids by those who hunt and collect them. “Those who love them love them madly,” Orlean writes (50). She shows how this is not a new phenomenon. In Chapter 5, she details the lengths people have gone to when collecting orchids.