What provoked a modern-day St. Valentine’s Day massacre?

On Valentine’s Day, four members of the Coverdale family – George, Jacqueline, Melinda, and Giles – were murdered in the space of 15 minutes. Their housekeeper, Eunice Parchman, shot them one by one in the blue light of a televised performance of Don Giovanni. When Detective Chief Superintendent William Vetch arrests Miss Parchman two weeks later, he discovers a second tragedy: the key to the Valentine’s Day massacre, a private humiliation Eunice Parchman has guarded all her life.