A 300-kilometer stretch of railway across Thailand carries both an engineering story and a wartime one. The film follows the trains and crews that still run this line today, tracking monsoon floods that wash out embankments, street markets that crowd right up against the tracks, and mountain passes that push 40-year-old steel locomotives to their limits. Woven through the present-day operations is the history of the line's most notorious section, the WWII "Death Railway" built along the River Kwai by Allied prisoners of war and forced laborers under Japanese command, a project whose human cost is now inseparable from the track itself. Engineers and rail workers explain what it takes to keep aging infrastructure running through terrain that seems built to defeat it, while the film uses the railway's physical challenges to keep returning to how it was built in the first place, and at what price. The result pairs a working-railway procedural with a wartime history lesson.