Conniving Shannon McBain arrived in Llanview in early 2004. Her mother had died from a long illness and her father had abandoned the family during her mother's aforementioned illness. Shannon was acting up at her college and rather than deal with expulsion, Shannon's aunt Eve helped her get a transfer to Llanview University, where Shannon could spend time with her aunt and cousins. Shannon became infatuated with River Carpenter almost immediately, and tried to break up his teen-dream romance with his virtuous girlfriend Adriana. Shannon's initial attempts went nowhere, so she teamed up with fellow schemer Rex Balsom, who lusted after Adriana. River enjoyed Shannon's company, but they never got past a few makeout sessions before River reconnected to Adriana and then abruptly moved to New York City to study at Julliard. By this time Shannon was more interested in trying to seduce Rex.
Due to failing a few classes, Shannon was forced to move in to a house with various other poor students (Marcie Walsh, Jen Rappaport, among others) and build a community center in order to get a passing grade. The community center was hit by a series of vandalisms, and all eyes fell on Shannon. While getting support from Rex (whom she was now having a fling with), and the trust of a few housemates like Marcie, she fought to clear her name. As Shannon stopped talking about the vandalism accusations, she was presumably cleared on the matter. Shannon tried to help Rex hide evidence in Paul Cramer's murder, but left town shortly after without even telling her family where she was going. Her family had to find out from Rex.