Behind-the-scenes look at the London Underground, beginning with weekend rail replacement works threatening to disrupt the daily service, and a woman pushed onto a live track during a busy Saturday night at Leicester Square. The number of passengers using the Tube at the weekend has doubled in the last decade, forcing the system to adapt to changing circumstances.

Following the work of plain-clothes ticket inspectors Diane McConnell and Denese Brunker as they pursue fare-dodgers across the network, fighting a crime that costs London Underground £20million a year. The pair confront some of the people who contribute to the 60,000 unpaid journeys taken every day, revealing what happens to those caught red-handed.

The work of emergency response units on the London Underground are taken a look at. Two drivers talk about the horror of seeing someone falling or jumping in front of their trains. The series also looks at how the underground deals with the demands of the annual Notting Hill Carnival.

Faulty doors and a signal failure cause major delays on the Victoria Line, where head of upgrades David Waboso is trying to work on a solution to the network's trebling of passengers over the past 10 years. Meanwhile, supervisor Barry Griffiths endeavours to keep the crowds moving at Tottenham Court Road as work continues to make the station six times bigger.

Rush hour is the biggest test on the underground and it can be too much for some passengers. Station Supervisor Bob Weedon at Bank has to deal with some injured passengers and faintings in a row. Chief operating officer Howard Collins has to step in and help following a power failure on the Jubilee Line that threatens to disrupt the evening rush.

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.