Going behind the scenes of the world's oldest, largest and busiest underground train network as it undergoes the biggest overhaul in its history.
For Tube drivers, their worst fear is somebody jumping or falling in front of their train. We follow what happens when this fear becomes a distressing reality for two drivers.
Also, we meet the crews of the Tube's specialised emergency response units as they are scrambled to deal with any eventuality on the Underground, from accidents and injuries to mysterious obstructions on the line. Plus how the Tube - and its dedicated British Transport Police officers - copes with the demands of the Notting Hill Carnival.