The dashcam of a passing car captures stunning footage of the final moments of a Taiwanese commuter aircraft as it banks steeply, clips an elevated highway and nosedives into the river. Investigators find no signs of pre-impact malfunction in either the plane's flight control or hydraulic systems. The search becomes even more complex when they study the wreckage and find the blades of the right propeller engine feathered, suggesting it lost power during flight. But the more clues the investigators uncover, the greater the mystery: What caused the propeller to feather, and why did the plane bank violently to the left just before impact?