This series follows more than ten thousand engineers and construction workers as they race to complete the brand new railway directly underneath the city - Crossrail, London's new Underground. Costing fifteen billion pounds, it is the biggest engineering project in Europe. Linda Miller, an engineer more at home constructing space launch complexes, must build what will become Britain's busiest station - Farringdon - an underground structure longer than the Shard is tall. Linda and her team battle ancient fault lines, race to build emergency access tunnels to alleviate congestion and piece together a giant geometric jigsaw that will form a cathedral-sized station entrance. The episode ends with a very special visitor arriving on site to give the railway its new title.