Portobello by Ruth Rendell

When wealthy Eugene Wren finds some money on the street, he decides to post a notice in Notting Hill to try and find the rightful owner. This act of kindness causes Eugene's life to intersect with some interesting characters. Petty criminal Lance Platt sees the paper and decides to try and get the cash, even though it's not his. Meanwhile, the real owner of the money, Joel Roseman, becomes infatuated with Eugene's fiancee, Dr. Ella Cotswold. Eugene also has problems of his own as he tries to control his addiction to Chocorange, a sugar-free candy. In Portobello, Rendell has created a vivid contemporary portrait of Portobello Road and Notting Hill and their inhabitants.