In 2009 market trader Kathy Green died after drinking drugged coffee. The UCOS team suspect but cannot prove a link with Anthony Gunnell, a man who raped women after doping them with coffee from his refreshment van. Through Helen, the nurse who looked after Kathy's senile mother in her last days, they learn that Kathy had an illegitimate daughter who was adopted and whose attempted reconciliation with her mother went badly. In solving the case Sandra recognizes parallels with her own unsatisfactory relationship with her visiting mother.
—don @ minifie-1