The Piccadilly Line is famed for its glamorous stops, which include Knightsbridge and the West End. Rob Bell discovers how the Piccadilly Line played an important part in saving the Tube from bankruptcy, as well as how it changed the face of public transport. He visits an abandoned station beneath Piccadilly Circus, where he discovers just what was needed to modernize this much-loved stop in the 1920s, when a surge in motorized buses drew passengers away.

London's Metropolitan Line was the world's first underground railway and is still used by 70 million passengers each year. Rob Bell discovers how the capital's overcrowding problem was the necessity that prompted this hitherto unthinkable transport innovation, which went into operation in January 1863, linking Paddington and a terminus at Farringdon. He fulfills his childhood dream of riding one of the original underground steam trains that carried passengers through tunnels and learns how unpleasant it must have been.

Engineer Rob Bell unearths the history of the Central Line, learning that Bank's platforms are curved to avoid the Bank of England's gold vaults. He investigates the most tragic night in the Tube's history: a disaster during the Second World War in which 173 people were killed at Bethnal Green station while seeking shelter from an air raid. At 46 miles, the Central Line is the longest of all tube lines, connecting east with west and transporting 260 million passengers a year, making it the busiest line in Britain.

The Northern Line was the world's first deep Tube line, running 36 miles and connecting the north and south of the Thames. Rob reveals the obstacles encountered and the innovations pioneered by the Victorian engineers who built it.