Penny (Masterson) is the older sister and only support for teenaged Mary (Malone), who suffers from cystic fibrosis. Penny is a jaded, pill-popping hooker while Mary, however, refuses to give up her optomistic outlook on life. With the aid of cantankerous neighbor Professor (Lindo) and a couple of new friends, Mary is determined to change Penny's views as well. Manages to skirt the subject's inherent sentimentality with some winning performances.