Sierra SixBy: Mark Greaney Series: Gray Man THE LATEST ALL ACTION THRILLER IN THE GRAY MAN SERIES SOON TO BE A MAJOR NETFLIX FILM. Before he was the Gray Man, Court Gentry was Sierra Six, the junior member of a CIA action team. In their first mission they took out a terrorist leader, but at a terrible price the life of a woman Court cared for. Years have passed and now The Gray Man is on a simple mission when he sees a ghost: the long dead terrorist, but he's