Zoe gets Dr. Lightman's help in a case involving an African-American college athlete accused of statutory rape, and Dr. Foster tries to help a sympathetic mother while investigating a religious leader for the IRS.
While on vacation in Mexico, Lightman and Emily become involved in the case of a missing American woman. Back home, Foster investigates tainted blood in D.C.-area hospitals with Lightman's rival, Jack Rader.
An old friend from Lightman's past comes for help, and gets Lightman involved with a dangerous man being investigated by the FBI. Meanwhile, the rest of the team tries to find the high schooler behind a dangerous and threatening video.
Agent Reynolds refuses to testify in an undercover case from his past because it may reveal that he killed a man during the operation, but Dr. Lightman tries to come to his defense and keep him out of harm's way.
Dr. Lightman is convinced that one of his former protégé's students is a sociopath connected to a woman's disappearance, but everyone else is skeptical. Meanwhile, Torres and Loker help a high school teacher who thinks he saw an UFO.
An Irish terrorist comes to Dr. Lightman to find out who killed his wife and daughter seven years ago, which reveals secrets about Lightman's relationship with Dr. Foster and his past job working counter-terrorism for the government.
Cal agrees to testify for the prosecution until he learns that his ex-wife is representing the innocent defendant: a beautiful younger woman accused of killing her much older, and extremely wealthy, husband.
Dr. Lightman helps Torres's half-sister, who is serving time in a juvenile facility, after an fellow inmate who asks for her help is killed. However, Torres is not convinced that her sister can be trusted.
The Lightman Group discovers that a governor's staffer who was killed during a rally right before the election may have been the target all along to protect a cover-up, and Clara might be lying to protect somebody on the inside.
The FBI investigates the murder of an illegal underground fighter, but Dr. Lightman tries to conceal his relationship to the event. Meanwhile Dr. Foster finds out discovers that her new boyfriend may have a big secret.
The Lightman Group helps a father find his daughter, who left home and became a porn actress, but Cal soon suspects that he's keeping something from him. Meanwhile, Eli and Ria compete for a promotion.