 After arresting an on the run rapist, a police dog discovers the body of a murdered girl, apparently raped. Upon discovering that she had indeed been sexually active, the police suspect her music teacher of having an affair with his student, the raped and killed girl. Benson and Stabler find that the raped girl s friend is having sex with their music teacher. The only reason Shannon, the raped girl, had been in her music teacher s apartment was to have sex with her boyfriend. They had to sneak around because their families had forbidden them to date. Then it is discovered that Shannon was pregnant, and the baby s genes were more than 50% Shannon s, there fore there had been incest.