When you scratch your chin, wring your hands, wrinkle your nose, or swallow too much, Dr. Cal Lightman knows you're lying. He doesn't just think so, he knows so, because he's taken his exceptional skills of observation to become the foremost deception expert in the country. Being a human lie detector, Cal can uncover the deepest secrets and crack the hardest cases. More accurate than any polygraph test, he knows when those in front of him are being less than forthcoming, be they family, friends, or complete strangers.
Cal heads up a private agency contracted by the FBI, local police, law firms, corporations, and private individuals when they hit roadblocks in their searches for the truth. Joining him are a variety of experts in the field of behavioral evaluation: Dr. Gillian Foster is a gifted psychologist and Cal's professional partner, a woman whose guidance Cal needs, whether he knows it or not; Will Loker is Cal's lead researcher, and he's so aware of the human tendency to lie that he's decided to uncomplicate matters and practice what he terms "radical honesty": he says everything on his mind at all times. Ria Torres, the newest member of the team, arrives at the truth differently by acting more on instinct and using her natural, less-studied ability to read body language and catch certain clues that Cal's other pledges may miss.