Dr. Cal Lightman (Tim Roth), the world’s leading deception expert, has developed a revolutionary new system using involuntary facial expressions and body language to determine if someone is being truthful, dishonest, or has something they're hiding.
Lightman spent years honing his skills, first working for British Intelligence in Northern Ireland and Yugoslavia, then the CIA, and later, the Pentagon; now he runs a private consulting firm, the Lightman Group. He and his team, Gillian Foster, Eli Loker, and Ria Torres work with law enforcement and government agencies, as well as other groups and individuals, to help them solve mysteries and crimes, do background checks, or any other job in which there's a dire need to determine if someone is being dishonest, and if so, to expose the truth behind the deception. FBI agent Ben Reynolds is a later addition to the team.
The premise of the show is based on the work of Dr. Paul Ekman, the psychologist who pioneered the study of emotions in relation to facial expression and body language, giving the show an air of realism.