The Millers are far from perfect. Childish Jake, his neurotic sisters Beck and Ashley, and their clueless mother Deborah find themselves under the same roof for the first time in years when their eccentric grandmother, Helen, dies. Little do they know what trials they will face when Helen's secret inheritance—the famed Florentine Diamond, a yellow gemstone that belonged to the Austrian Empire and disappeared a century ago—enters their lives.

With no idea how one of the world's most mysterious diamonds ended up in Helen's bedroom, they begin to explore her past and realize how little they know about their courageous grandmother's remarkable life and the complex, intertwined history of their family.