Contains spoilers for this episode and earlier episodes.
During a university lecture, student Martin Walker challenges Lightman's ability to read him and wins their public wager. Lightman suspects he has met a dangerous man, but the student's teacher Helen, once Cal's own teacher and lover, resists his conclusions. A missing student's case and the death of Martin's sister draw him further into the investigation. Gillian worries that his history with Helen is distorting his judgment.
Torres helps an escaped abductee speak about being repeatedly waterboarded, linking Martin to her captivity. Martin approaches Torres too, then reacts violently when Helen ends their relationship. He abducts Lightman, tortures him and forces him to dig a grave in the woods. Lightman draws him into admitting that he watched his sister drown because he wanted her bicycle. Reynolds and the police arrive before Cal is killed, and the search uncovers other victims buried nearby.
Loker and Torres also investigate a teacher threatened with dismissal after reporting a UFO. A student's recording supports the fact that he saw something, while a military officer explains it as an aircraft incident that officials concealed. The team finds a compromise that saves the teacher's job without making the footage a public explanation of everything that happened. Afterwards, Gillian acknowledges that her suspicions about Cal and Helen made her slow to recognise the danger posed by Martin.