Bill Whitaker takes a hard look at the U.S. electric grid – the largest machine in the history of the world, a hodgepodge of public and privately-owned companies cobbled together over generations – so essential to daily life that we literally couldn’t live without it. 60 MINUTES’ investigation into the threats facing the grid, from cyber-attacks to sabotage and physical assaults, are eye-opening and not reassuring. What’s more, no U.S. government agency, not even the Department of Energy, is truly in charge of protecting it. Graham Messick is the producer.

Lesley Stahl visits Fred Miller and his family in the large house in southern Virginia that they recently bought to host family gatherings, only to discover that their own ancestors had once been enslaved on that very property. Miller’s sister and cousins scoured historical records and enlisted a genealogist to find evidence that their great-great-grandparents, Violet and David Miller, were enslaved on the plantation, then-called Sharswood. The dilapidated building still standing behind the main house has been identified by archeologists as living quarters for some of the enslaved men and women there. Buying this home has opened a window into the Miller family’s past that was not discussed within their family, and that many African American families struggle to obtain. This is a double-length segment. Shari Finkelstein is the producer.