London is getting bigger - and its 150-year-old underground network has to keep up. This eight-part series meets the staff working to make that happen, including station supervisor Tony, who this week unveils a controversial solution to an escalator overcrowding problem at Holborn. Line service controller Charlotte reveals the incredibly precise timing that keeps the Piccadilly line running, and an Arsenal home game causes chaos at Highbury & Islington station when fans and commuters collide at rush hour. A fascinating look at the effort, energy and composure required to run something the capital takes for granted.