Going behind the scenes of the world's oldest, largest and busiest underground train network as it undergoes the biggest overhaul in its history.

Every night, 10,000 workers descend on the Tube to maintain, repair and clean it. We follow this invisible overnight army as they work against the clock in the four-hour window when the power is off - from hard-working Bulgarian cleaner Vladimir, who is amazed that the British government pays for people not to work, to 23-year-old Harry leading his gang of 'fluffers' picking fibres and lint from the tracks. Meanwhile, pest controller Mick is called to a smelly problem at Hounslow Central, while emergency response worker Roy gets inside one of the Underground's disused 'ghost' stations, Down Street. Show less