In the Shadow of Diablo - Mystery of the Great Stone House alternates between a local teacher's present day adventure and the historical accounts of the brutal murder of Dr. John Marsh, one of the most important figures in California history. Harrison Barrett is a Brentwood science teacher who is compelled to investigate the sudden and tragic suicide of one of his high school students. Along with colleague Celeste Scott, Harrison finds himself engulfed in the legend of a hidden treasure and entwined with the real-life tale of a distraught son - Charles Marsh, whose father was slain 150 years prior. Past and present are linked as Charles seeks justice and Harrison searches for answers. The journeys of both men are filled with mystery and intrigue, separated by generations but united by a common yearning, a common motive... and a common setting - the shadow of Diablo.