Mulder and Scully assist Cleveland Detective Alan Cross with the investigation into a brutal homicide in which a female victim's body is so badly decomposed, and covered with a mucus-like slime, that positive identification is difficult. Mulder connects the case to a series of similar killings in which female victims-all of whom answered personal ads in local newspapers-died in a similar manner. When the latest victim, Lauren Mackalvey, is identified, Mulder locates her roommate, Jennifer. Jennifer explains how Lauren meet her date on the Internet, a man who went by the on-line name "2Shy." Meanwhile, Scully's autopsy on Lauren's body reveals that a great deal of her body fat is missing.
     Meanwhile, when the killer, Virgil Incanto, gets stood up by his on-line date, Ellen, he attacks and murders a prostitute. During the struggle, the prostitute scraps Virgil with her nails, leaving rake marks on his arm.
     Mulder examines the killer's e-mail correspondence to Lauren. He discovers quotations from rare Italian poems, leading him to believe the suspect is a college professor or translator. Cross assembles a list of people in the Cleveland area with such credentials. Chemical analysis of the killer's skin sample found beneath the prostitute's fingernails shows no oils or fatty acids-leading Mulder to speculate that the murderer might be using his victim's bodies to replenish a chemical deficiency in order to survive.
     Meanwhile, using Cross's list, the agents interview possible suspects. But it is Cross who ends up interviewing Virgil, and in the process, notes a bandage on his arm. Virgil kills Cross, then arranges another date using the Internet. When his intended victim, Ellen, drives him home, Virgil spots someone inside his apartment. He hastily excuses himself. Virgil's nosy landlady, Monica, discovers Cross's decomposed body inside the apartment. Virgil kills Monica before she can scream. But Monica's blind daughter, Jesse, enters Virgil's apartment looking for her mother. Though Virgil insists Monica is not in the apartment, Jesse smells her mother's perfume. Jesse calls 911, and the agents rush to the apartment building. But Virgil is not to be found.
     The agents access Virgil's computer records, hoping to find clues about his next victim. Meanwhile, Virgil talks his way into Ellen's apartment, apologizing for his hasty exit during their date. As Ellen sends a computer message to an on-line friend, a message from the F.B.I.-warning about Virgil-pops up on her screen. Virgil sees the message and attacks Ellen. After cracking Virgil's computer hard drive, the agents contact women who are his potential next victims. Unable to reach Ellen by phone, the agents drive to her apartment. Mulder and Scully, acting on a tip from a neighbor, burst into Ellen's apartment. As Mulder searches for Virgil, Scully stays behind with Ellen, who is covered with mucus but still alive. Suddenly, Virgil springs from the shadows and attacks Scully. Ellen, however, regains consciousness, and shoots Virgil. Virgil recovers from the gunshot wound, and is later interrogated.