James Marsh does not hide the ending. He hides the route.
His films often begin with a fact already sealed by history: Philippe Petit walked between the Twin Towers; a chimpanzee was raised as a human; Elvis became an American myth. The dramatic engine is not what happened? It is how could this have happened—and what did it cost?
Marsh converts outcome into inevitability, then makes every obstacle between the audience and that outcome feel newly dangerous.