In Season One, 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 is so aware of the human tendency to lie that he has 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.
Dr. Cal Lightman is the world's leading deception expert who studies facial expressions and involuntary body language to discover not only if someone is lying, but why. Lightman and his team of deception experts assist law enforcement and government agencies to expose the truth behind the lies.
The son of a family of devout Jehovah's Witnesses is accused of killing his teacher after being caught fleeing the scene of her murder. Meanwhile, the team is hired by the Democratic National Committee to investigate a second case in which the Chairman of the House Ethics Committee is accused of paying for sex.
When a female soldier accuses her commanding officer of sexual assault, Lightman is brought to Fort Meade to find out if there's any truth to the accusation. The woman is found to be covering for someone else. Lightman tricks the officer into admitting that he coerced sex with a cadet by threatening to give her the most dangerous assignment.
Meanwhile, Foster investigates whether a high-profile basketball recruit accepted bribes to play for a university.
The murder of a teenage girl who is the daughter of a powerful federal judge leads The Lightman Group to a highly competitive college-prep school where getting to the head of the class means everything. Lightman discovers that a fellow student killed her to protect her involvement in an SAT cheating scam.
Foster investigates a NASA test pilot accused of intentionally crashing a $250 million aircraft.
A controversial South Korean ambassador is presumed to be an assassination target at his son's state wedding. The Lightman team is sent to prevent the murder. Yet the son is shot instead and Lightman exposes long-held family secrets and lies in order to identify the killer -- the jealous ex-husband of the son's wife who was using the potential threat at the lavish affair as a cover.
Lightman and Torres team up to interrogate a notorious and imprisoned gang leader who claims to be rehabilitated. If the gang leader is freed on parole, he might help fight inner-city violence or return to his life of crime.
Foster and Loker investigate the death of a firefighter who was killed in the line of duty. He may have been murdered in a hazing prank gone wrong, but it is revealed that he violated a fireman's code by sleeping with the chief's niece.
Lightman and Foster investigate the disappearance of an 11-year-old girl who may have been murdered. When she is eventually found, the girl refuses to reveal any information about the kidnapper. Lightman finds that she is protecting another victim that's currently being held by the same captor.
Meanwhile, Loker and Torres must determine whether a famous peace activist has lied about her meager upbringing and is who she claims to be in her bestselling memoir. This may jeopardize her global standing, but Loker's attraction to the socially conscious woman may be clouding his assessment of her.
A good friend of Lightman's asks him to find out who stole confidential research from his pharmaceutical company. Lightman must weigh the loyalty to his friendship when he discovers a high-level conspiracy surrounding a new drug that could put thousands of lives at risk.
The team is also hired by the State Department to assist in negotiations for the release of two Americans imprisoned in Yemen.
Lightman becomes obsessed with finding a link between two young women who committed suicide. More is learned about what drove him to study micro-expressions: the death of his mother.
Foster and the team try to recover billions of dollars for investors in a teachers' union pension fund who were bilked by a Ponzi scheme.
Workers are trapped underneath a collapsed building in a small town outside Washington and everyone lies to cover their culpability. Lightman is brought in to determine who is at fault, and he discovers a massive cover-up.
The team is hired by an internet billionaire mogul who wants to see if his fiance's motives for marrying him are legitimate
Assistant U.S. Attorney Zoe Landau -- Lightman's ex-wife and Emily's mother -- brings a case in. She wants Lightman to help investigate a serial arsonist case in which the only key eyewitness is a 5-year-old boy. While Zoe gives glimpses about what it's like being married to a human lie detector, it quickly becomes clear that she and Lightman still have feelings for each other.
Meanwhile, Foster and Torres are immersed in the world of rival rap groups when one rapper gets killed in a drive-by shooting.
Lightman investigates a possible cover up by the police in the shooting of a potentially innocent teen. The case reveals to be bigger than it seems when the FBI is looking internally to root out a terror suspect within the DC police. Lightman must weigh whether to sacrifice an innocent kid for a potential national security risk.
Meanwhile, investors who were bilked by a Ponzi scheme are suing The Lightman Group for botching the recovery of their money.
FBI Agent Ben Reynolds has been pursuing a serial rapist who is terrorizing the Washington area. He reluctantly partners with The Lightman Group to track down information from a convicted criminal who the rapist seems to be copy-catting. Lightman infiltrates a prison to befriend Andrew Jenkins, a pathological liar who seems to stump even the mighty Lightman. The serial rapist may be Jenkins' protege.
As Torres and Loker search Jenkins' fan mail, Foster questions one of the rapist's recent victims. Foster is attacked by the rapist, which leads the team to discover the unlikely culprit.
Lightman asks for a permanent police presence in the firm, meaning Agent Reynolds might be working with The Lightman Group again.
Domestic terrorist bombings are occurring across the Washington, DC area sending everyone in a panic. FBI Agent Ben Reynolds calls on The Lightman Group to help identify those responsible and prevent more attacks. Lightman finds that the bombs were detonated remotely and that the bombers were set-up by someone else.
The case takes a personal turn for Torres when Dupree goes missing. Lightman decides to hide the news from Torres so she can remain focused on the big picture. Is honesty indeed the best policy?
Zoe helps Lightman with the investigation and both are concerned about their daughter's safety.