Dan Snow travels the English south coast by land, sea, and air with D-Day historian Stephen Fisher, tracing the physical remains of Operation Overlord before the story even reaches Normandy. More than 150,000 Allied troops crossed the Channel on 6 June 1944 to storm five beaches against Hitler's Atlantic Wall, and this film argues the invasion's real origins sit across the Solent, where concrete embarkation hards, sunken landing craft, and abandoned training grounds still mark the coastline. Snow and Fisher visit these sites directly, reading the preparations for the largest combined air, land, and sea assault in history out of what was left behind rather than archive footage alone. The pair inspect wreckage below the water as well as structures on land, piecing together how southern England was transformed into a staging ground for the invasion fleet. It is a coastline tour built around physical evidence, with Fisher's expertise anchoring each stop in the wider Overlord planning.