On Beauty centres on the story of two families and their different, yet increasingly intertwined, lives. The Belsey family consists of university professor Howard, a white Englishman, his African-American wife Kiki, and their children Jerome, Zora and Levi, living in the fictional university town of Wellington, outside Boston. Howard's professional nemesis is Monty Kipps, a Trinidadian living in Britain with his wife Carlene and children Victoria and Michael.
The Belsey family has always defined itself as liberal and atheist, and Howard in particular is furious when his son Jerome, a newly born-again Christian, goes to work as an intern with the ultra-conservative Christian Kipps family over his summer holidays. After a failed affair with Victoria Kipps, Jerome returns home. However, the families are brought into proximity again nine months later when the Kippses move to Wellington, and Monty begins work at the university.
Carlene and Kiki become friends despite the tensions between their families. Rivalry between Monty and Howard increases as Monty challenges the liberal attitudes of the university on issues such as affirmative action. His academic success also highlights Howard's inadequacies and failure to publish a long-awaited book. Meanwhile, the Belsey family is facing problems of its own, as they deal with the fallout of Howard's affair with his colleague and family friend Claire.
Zora and Levi both become friends with Carl, an African-American man of a poorer background than their own middle-class lifestyle. Zora uses him as a poster child for her campaign to allow talented non-students in university classes. For Levi, Carl is a source of identity, as a member of a more "authentic" black culture than Levi considers his own background to be.