A car stops in the woods at night. After cutting though a chain-link fence, a man opens the trunk; there's a woman bound inside. He grabs a shovel and starts digging. Meanwhile, the woman frees herself, climbs out, and runs away.
While Cal speaks at a local college, a student named Martin Walker challenges Cal's ability to judge facial expressions, so Cal bets $100 that he can read Martin's reactions to random photos. The first one is a pretty girl. Cal says Martin shows revulsion, but he's wrong! Cal doubles the bet. The second is a torture scene, which Cal says arouses Martin. Wrong again!
After class, Cal tells the professor, Helen, that Martin fooled him the first time because he's a psychopath and he let Martin win the second round. Cal then asks about any recent missing person cases in the area and learns there was a girl who disappeared last month. Cal also tells Gillian that Helen, who was his professor (and lover) at Oxford, and Martin have a romantic relationship.
Meanwhile, Eli and Ria question a high school teacher named Mr. Hixon whose job is in jeopardy because he reported a UFO sighting. But Hixon truly believes what he saw, adding that people are always trying to explain away the unexplainable.
Cal and Ben trail Martin to a restaurant, where he quickly spots them. The next day, Martin comes to the Lightman Group office, where he denies Cal's psycho-killer allegations. Cal says Martin's not as clever as he thinks. Martin sneers that he's not only patient, he's also always five moves ahead.
Cal's response is to put up warning flyers with Martin's photo on them all over campus. Gillian, who's unconvinced, asks Helen if Cal was always like this. Worse, says Helen.
When Eli and Ria question Hixon's students; one, Andre, shows great regret. Turns out that he shot video footage of the UFO. Eli wants to give the video to the local media.
Cal and Gillian question Martin's mother about her son, but Martin shows up and orders them out. Cal tells Gillian that Martin's mother is afraid of him. Gillian says Cal has unresolved conflicts with Helen.
Back at the office, Cal shows Gillian a home movie of Martin and an older sister that he stole from the family home, noting there were no photos of the girl in the house. Ben reports that Martin's sister drowned in the family pool when she was seven and that Martin, then five, witnessed this. Ben also explains that a local college student named Valerie was recently abducted and escaped, but she suffered a mental breakdown and isn't talking.
Then Martin literally bumps into Ria at a coffee shop, replaces her spilled drink, and invites her to a concert. Ria agrees to go, but Martin explains Cal's suspicions about him, and Ria takes off.
Gillian and Cal are visiting Valerie in the hospital when Ria arrives and tells Cal what just happened. Cal sends Ria into to bond with Valerie, who says Martin water-boarded her to near-death, revived her, then repeated this again and again.
Ben brings Martin in for questioning by Cal. While Martin admits that Valerie was in his car, he claims Valerie came on to him and she was using antidepressants. Cal says that's because Martin preys on the weak. Martin says he prefers strong women, like Helen. Cal asks if that's because he likes to be dominated and Martin gets angry, then flashes a smile. We see a similar expression on famous photos.
Meanwhile, Ria is looking at pictures of famous con artists, when Hixon interrupts -- Eli told him about Ria's encounter with Martin -- and says that once you're able to lie to yourself, it's easy to deceive others. And there's no explanation for Martin's behavior.
Then a Colonel Gorman arrives and tells them that the night of Hixon's UFO sighting, a nuclear-armed B-1 bomber pilot suffered a mental breakdown, flew off-course, and was shot down off the coast. That's what Hixon saw, and in the interest of national security, they kept this quiet. Eli knows the Colonel's story is true, but it's still a cover-up, and the Air Force will never admit to a violation of U.S. airspace.
Helen tells Martin their relationship is over. He claims Cal's behind this and attacks her, but she's saved by a phone call. Martin exits; Cal enters. Helen warns Cal that Martin will be coming after him.
When Helen leaves, she notices Martin's car following her. She immediately phones Cal, but Martin's already got a gun to his head. Martin abducts Cal, water-boards him, and takes him to the woods, where he makes Cal dig a grave. Cal asks about Martin's sister. Martin admits watching her drown because he wanted her bike.
Then Ben and the police arrive. Cal noticed Martin kept looking at a certain tree and suggests they search that area for bodies of other victims, which they find. Cal also asks Martin for his $200 back.
Back at the office, Ria and Eli discuss the compromise story that saved Hixon's job. As for the UFO footage, Ria says, "I don't think it's a mystery anyone can solve."
Meanwhile, Gillian admits to misreading Martin because she thought Cal was still obsessed with Helen. Cal says he understands, then asks if she wants to get dinner. Gillian has work to do. Cal leaves.