A security guard, Jeff Zegers, follows a young woman who has been shoplifting up and down 5th avenue into the dressing room, only to be fatally shot. Danny finds a dental mirror and burned off security tags by the body, and Adam is able to zero in on a woman wearing a reflective coat on surveillance videos. The CSIs follow her trail, interviewing a shop girl named Marissa Richardson, who their mystery thief stole a $25,000 purse from. When the shoplifter strikes again, this time stealing men's items, Stella realizes they're dealing with a professional thief. The CSIs view the newest surveillance footage and see the woman licking her finger to slide a ring onto it. They get the ring from the store--which proves to be a fake switched in by the thief--and get DNA off of it. Though the sample is unknown, the levels of a drug called propanolol in the sample indicate she's part of a medical trial, and through the records, they are able to identify the shoplifter as Ava Brant.
The body of a Chelsea University college student is found beaten and stabbed in a hedge maze in Queens with exam slips with two different names on them. Both boys, Eddie Williams and Thomas Brighton prove to be alive, and Eddie identifies the dead boy as Brian Miller. Both Thomas and Eddie, a pre-med student who is also Brian's roommate, admit that Brian took tests for them. Mac is surprised when Reed Garrett, the son his wife Claire gave up for adoption, comes to him and tells him that he and Ryan were colleagues on the college paper, and that Brian was writing a big expose on a secret society on campus known as the Knights and Shadows. Mac and Flack zero in on Thomas Brighton, a member of the Knights and Shadows. Thomas claims not to know anything about the article, but admits Brian was a member of their group. He underwent their exit ceremony that night when he told the group he wanted out, and though the ceremony involved a beating, Thomas swears they left Brian alive.
After Reed, who was working on a story exposing college kids helping others cheat on their exams, is beaten, Hawkes discovers radioactive material on a scrap of fabric found in one of the bushes near Brian and connects it to med student Eddie. Eddie confesses that he killed Brian after learning about the expose story Reed was writing. Eddie hoped to cash in on the university clause that gives straight As for the semester to any student whose roommate dies. He also beat up Reed, who tells Mac at Brian's funeral that he wonders if he could have prevented Brian's murder.
Danny and Stella track Ava Brant down, but she denies killing Jeff, something Adam backs up when he finds a sophisticated device that reads credit card numbers from a distance in the $25,000 bag. This leads the CSIs back to Marissa Richardson, the shop girl who showed Ava the bag. She conspired with an ex-con named Chris Campbell to swipe credit card information from wealthy customers and defraud them, but Jeff caught on to their scheme and wanted in on it. Chris lured him into the women's dressing room and shot him. Ava is off the hook for murder, but not grand theft. Stella compassionately suggests the women reveal her past abuse at the hands of her husband, to get leniency from the judge, and offers Ava her card if she wants to talk.