This series follows a team of more than 10,000 engineers and construction workers as they race to build a brand new railway under London - Crossrail - London's new Underground. Costing fifteen billion pounds, it's the biggest engineering project in Europe and a huge challenge to pull off. As they burrow the 42km of tunnels, engineers must battle to make sure that listed buildings don't crack, London Underground trains keep running, roads don't shut and the City stays in business. Crucially, they must drive one of their gigantic 1,000-tonne tunnel-boring machines through a tiny gap in the congested underbelly of Tottenham Court Road station without the passengers on the tube platforms below knowing they are there.

This episode follows engineers building London's brand new underground railway, Crossrail, as they race to build ten new train stations across London.

A team battles to put together the giant jigsaw that will become a cathedral-sized station at Canary Wharf. It's so big, they have to build it in a dock and underwater. Its architect-designed roof is so complicated it comes in a kit of over 2,500 pieces. As engineers carve out the underground caverns that will become the new stations, they hit on some gruesome discoveries of London's past.