Documentary filmed over the course of a year going behind the scenes on the London transport network as it undergoes a £10bn modernisation programme to cope with record demand. At Earl's Court station, Charlotte controls the Piccadilly Line, one of London's busiest, oldest and most unreliable lines, while new recruit Naeem faces furious passengers at Bank station when a strike hits the network. Tino from the special requirements team is sent to Highbury and Islington to deal with one of the Tube's worst nightmares as rush hour coincides with a football derby.

The closure of the ticket office at Victoria station creates problems as all passengers requiring a ticket or a top-up have to use just four machines, while at Greenford station a new multimillion-pound prototype lift that travels sideways as well as vertically is being installed. At Waterloo, 72-year-old customer service assistant Philippa has decided to retire and several regular travellers find the time to present her with gifts as she steps down.

At Leicester Square station, customer service assistants Ric and Kingsley are faced with crowds of ghosts, ghouls and demons as Halloween partygoers pass through, while the emergency response team is sent to St John's Wood after passengers report hearing gunfire. Meanwhile at King's Cross, engineer Pete leads a massive weekend track-replacement operation, but he and his team hit an unexpected problem.

At the busy Bank station, customer service assistants Eamon and Ian face an epidemic of patrons dropping phones, wallets and Oyster cards onto the tracks and must bring trains to a halt to retrieve their belongings. Duty reliability manager Ricky is asked to examine the case of a passenger who complained after a train pulled out even though her clothes were stuck in the doors, while incident response team manager Richie has to redirect travellers at Cannon Street after a man is taken ill.

Staff face their busiest and most unusual shift on New Year's Eve, the only night when trains run for 24 hours and a million passengers are expected to be using the network. At Piccadilly Circus, customer assistants Lewis and Rory have to deal with passengers relieving themselves on the escalators, while almost 200,000 people are pouring through the gates of Embankment to watch a firework display. In the central control room, senior operating officer Dan gets a report of a suspect package on Waterloo Bridge, while incident response manager Richie is called out to an apparent stabbing at St Paul's.

Management has decided to crack down on fare dodgers and revenue inspectors Simon and Paul have to deal with an aggressive passenger refusing to pay at Angel. John is supervising the tricky restoration of Eduardo Paolozzi's famous mosaics at Tottenham Court Road, the installation of a new escalator is causing bottlenecks at Walthamstow and actress Barbara Windsor becomes a Tube driver as part of London Poppy Day.

The network takes on more than a thousand new staff, with applicants including would-be driver 54-year-old Danuta, who needs to get a grip on the details of signals and points, as well as the finer aspects of engine technology. Alice is hoping to be a customer service assistant, but first she must undergo an intensive five-week training course, while Naeem is halfway through his six-month probationary period and is working at the busy Bank station. In Dartford, a disaster training scenario unfolds as 2,000 staff cope with the simulated collapse of a tower block onto Waterloo station.

After two years of work, engineer Anita and her team are about to break through a concrete wall separating her new passenger tunnels from those of Crossrail, the giant east-west rail link being built across the capital. Meanwhile, the network takes delivery of 192 multimillion-pound trains, which are put through the `rattle test' before being pressed into service, while customer service assistant Stan prepares to say goodbye to the Underground after 35 years' service. Last in the series.