Adrienne opens by declaring that everybody lies. To support this belief, Adrienne describes a past psychological experiment involving a broken vending machine that dispensed candy while returning each subject's dollar.

Adrienne explains that the machine carried a posted phone number for reporting malfunctions, but the number secretly reached one of the study's researchers. Although every subject benefited from the error by taking free candy, not one person called to report the problem, which Adrienne presents as proof that dishonesty is universal.

After establishing this example, Adrienne shifts to her professional authority as a trained psychiatrist. Adrienne lists common signs of lying, including fidgeting, changes in voice or speech, and giving excessive detail in an effort to sound convincing.

Adrienne contrasts human observation with lie-detecting machines, noting that even the best machines make mistakes. Adrienne insists that she is more accurate because, when patients sit in front of her, she can read facial expressions, eye contact, gestures, and vocal changes that audiotapes cannot capture.

The prologue ends with Adrienne's absolute confidence in her own judgment. Adrienne claims that she always knows the truth and issues a blunt warning: no one should ever lie to her.