In episode one, "Fortress Britain", Cruickshank visits the sites of some little-known invasion attempts. In episode two, "The Bogeyman Is Coming", Cruickshank looks at Britain's response to the threat of French invasion by Napoleon's army in 1804. In the final episode, "Battle for Britain", Cruickshank examines how Britain reinvented itself as a fortified encampment under the threat of German invasion during World War II.