Sophomore year at Hawthorne College begins with an unpleasant surprise for Roni, Stacy, Sam, and Maddie. Instead of rooming together as they had planned, they've been split up—each has been paired with a freshman "little sister." Baby-sitting is hardly what the girls had in mind, but it's too late to try to change things now.
Maddie's freshman roommate, Erica Martin, turns out to be pretty, charming, and bright, the kind of girl who's an instant success wherever she goes. Maddie actually likes being her big sister—until Erica starts turning her charm on Maddie's new boyfriend.
All's fair in love and war, Maddie decides. With the help of Robi, Stacy, and Sam, she's determined to teach her adorable "little sister" the difference between right and wrong—the sooner, the better.