Tim and Siddy go under the platforms of Paddington station. It has five different tube lines running through it, with its oldest and newest lines opening 150 years apart.Tim dusts off the old Mail Rail line which used to transport post under London to sorting offices across the capital, and Siddy discovers some former police cells underneath the platforms, and unearths what remains of the luggage carousels from when passengers on the Heathrow Express were allowed to check-in their luggage in the main station.At Tottenham Court Road, Siddy reveals the huge changes to the station to accommodate the Elizabeth Line, and tells the story of how the station's iconic mosaic artwork was preserved during the works and takes us behind a locked door to uncover a floodgate installed as part of Britain's Cold War defences.At the London Transport Museum depot, Tim meets a young tube driver, who's built up a large following on social media for her posts showing behind the scenes of her job.