Denver, CO, 1955. When United Airlines Flight 629 bound for Seattle explodes in mid-air, killing everyone aboard, the new-to-air travel nation grieves over the terrible tragedy. But crash investigators find a few strange inconsistencies. There is the strange, sulphuric smell of the burnt aircraft bits, with other bits of the plane strangely left intact, odd testimony from the baggage handlers, all leading investigators to wonder if it was an accident at all. In a pre-TSA, pre-Black Box world, it takes months of painstaking police and FBI work to uncover a truth that no one can wrap their heads around: the first-ever act of sabotage to a commercial airline in the United States.