Cocktail Party Physics:

The novel’s subplot — fans might argue it’s the main plot, cleverly shrouded in the poison pen mystery — revolves around Harriet’s struggle to reconcile her feelings for Wimsey, and desires as a woman, with her fear of losing her hard-won individual identity and independence… a not-insubstantial concern for women of that era, especially those, like Harriet (and Sayers herself), of high intelligence. That tension finds the perfect musical metaphor in a scene set in a small antiques shop, where Harriet has allowed Peter, for the first time, to buy her a gift (a set of antique ivory chessmen that has captured her imagination). Wimsey spots an old spinet piano in the shop, and knocks out a couple of tunes… It is here that he makes his famous observation about preferring counterpoint to harmony.