The film revisits a notorious case that is still evolving, the one in which a New York City police officer named Gilberto Valle was accused of planning to kidnap women, then cook and eat them. What makes the case doubly bizarre is that at the heart of the preposterous-sounding charges are serious and sobering issues: Is it illegal to think vile thoughts and chat about them on the Internet? Where is the line between sadistic fantasizing and imminent crime?