For over two years, residents of Mosul lived under ISIS rule before Iraqi forces, backed by American air power and advisers, moved to retake the city in an assault that military commanders called the most intense urban combat since World War II. This FRONTLINE report follows soldiers of the Iraqi special forces and ordinary citizens through the street-by-street fighting, using footage shot amid collapsed buildings, sniper fire, and civilian evacuations to show what retaking a city of over a million people actually costs. Interviews with commanders and residents fill in what the footage cannot: the calculations behind targeting decisions, the fear of booby traps left behind by retreating fighters, and the toll of nine months of siege on families trapped in the Old City. The film traces the campaign from its opening push through the collapse of ISIS control, without glossing over the destruction left in the fighting's wake. It is a ground-level account of one of the defining battles against the Islamic State.