At Blaenavon, Wales, the Time Team goes looking for a railway viaduct that vanished from the historical record by 1815, a ten-arch structure built at the start of the Industrial Revolution and then buried under an estimated 10,000 tons of debris. The crew brings in heavy excavation machinery and ground-penetrating radar for what the show calls its deepest dig yet, cutting through decades of spoil to reach stonework nobody has seen in two centuries. A remote camera lowered into the excavation delivers the first live look at the buried arches, and the team pairs the dig with a wider look at the ironworks that made Blaenavon an industrial powerhouse, including the brutal working conditions inside the furnaces and foundries. Specialists walk through what the viaduct's design reveals about early railway engineering, still being worked out by trial and error at the time. The episode follows the team's usual mix of digging, on-site analysis, and expert interviews, building toward the moment the structure finally comes back into view.