Alice Roberts, Danielle George and Onyeka Nubia tell the complex story of Britain's obsession with invasion throughout its history. To illustrate the long history of these fears, they combine their expertise and make use of a range of different sources and methods. Along the way, they visit sites including the castles and mighty warships that sought to protect Tudor England and also learn more about how Britain's Home Guard planned for a nightmarish invasion of the country by Nazi Germany centuries later.