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.