Michael Portillo ventures deep underground onto London's newest railway: the Elizabeth Line. Emerging into the sunshine in Bedford Square, he recalls the choking smogs which plagued the capital during the 1950s. Back on the Elizabeth Line, Michael travels east to Stratford to visit the Theatre Royal, Stratford East, where pioneering director Joan Littlewood produced groundbreaking plays such as Oh! What a Lovely War. At Shenfield, Michael transfers to the Epping Ongar Heritage Railway. His destination is a nondescript 1950s bungalow, which hides the entrance to an underground bunker designed for use in the event of nuclear war.