London is built from concrete, steel and the creative urge. Old technology gives way to the new. Progress is inevitable - but is it more fragile than its inhabitants realise? A strange anomaly is uncovered in the new top-secret Crossrail extension being built under Buckingham Palace. It is an archeological puzzle, one that may transform our understanding of history - and the origins of London itself. And if our modern world falls, we may have to turn to the technology of the past in order to save our future.