Lightman becomes obsessed with his investigation of two young women who committed suicide. Meanwhile, the team tries to recover billions of dollars for investors who were bilked by a Ponzi scheme.

When Assistant U.S. Attorney Zoe Landau, Lightman's ex-wife and Emily's mother, enlists Lightman to help investigate an arson case in which the only eyewitness is a 5-year-old boy, it quickly becomes clear that she and Lightman still have feelings for each other. Meanwhile, Foster and Torres question a rapper who is suspected of murder.

The Lightman Group gets embroiled in the controversial case of a policeman who shot a potentially innocent teenager. Meanwhile, investors who were bilked by a Ponzi scheme are suing The Lightman Group for botching the recovery of their money,

Ben Reynolds, an FBI agent who's been pursuing a serial rapist terrorizing the Washington area, partners with The Lightman Group for its toughest case yet. Lightman infiltrates a prison to befriend Andrew Jenkins, a convicted criminal and a pathological liar who the serial rapist may be copy-catting. Meanwhile, Torres and Loker search Jenkins' fan mail, and Foster questions one of the rapist's recent victims.

After a terrorist bombing outside of Washington, DC, FBI Agent Ben Reynolds calls on The Lightman Group to help identify those responsible and prevent more attacks. The case takes a personal turn for one member of the team and begs the question of whether honesty is indeed the best policy. Zoe helps Lightman with the investigation and both are concerned about their daughter's safety.