In the spring of 2002, acclaimed filmmaker Joe Berlinger (Brother's Keeper, Paradise Lost, Metallica: Some Kind of Monster) travelled to Vienna to witness the burial of the preserved brains of over 700 handicapped children. The victims had been murdered in a "euthanasia" clinic as part of the Nazi eugenics program that many consider the opening act of the Holocaust.

Gray Matter chronicles the director's journey as he searches for Dr. Heinrich Gross (notoriously nicknamed "the Austrian Dr. Mengele"), who not only allegedly participated in these murders, but also continued to experiment on the children's remains for decades after the end of the war, while rising to prominence in Austrian society despite his past. Along the way, Berlinger meets clinic survivors and other remarkable voices who shed new light upon this shadowy legacy and the nation that now grapples with its own denial.

Why has it taken so long to bury these brains? Should science profit from knowledge gained from such immoral atrocities? How has Dr. Gross evaded justice for so many years? The film raises provocative questions about the nature of guilt, redemption and denial.