Tim and Siddy get access to the maintenance depot at Northumberland Park, responsible for looking after the entire fleet of Victoria Line trains. Tim meets the team checking all the carriages, and sees the incredible precision needed to finely shave the metal wheels to keep them running smoothly on the tracks. Siddy checks the vintage control panel on the tower and finds it is still in working order. They ride on the private service that links the depot with Seven Sisters station alighting at its mysterious third platform. At Finsbury Park station on the Victoria and Piccadilly lines, Siddy does a night-time track walk to access the now-disused tunnel which was part of an early experiment to run large electric mainline trains on the tube. At our Museum Tim hears about the importance of design across the tube network, and looks at the bespoke designs for seating fabric across different underground lines.