Plot: In the first of a bumper two-parter episode, the team hitch a ride on a battery locomotive as it weaves its way across the network deep into the night, learning about the specialist kit it carries to perform a challenging but rewarding job. Chris Nix, Laura Hilton Brown and Alex Grundon meet the crew who drive and coordinate these rarely spotted vehicles, and the team gets an exclusive front-seat view of a stretch of London’s Underground that you won’t see on any regular commute