Iain Stewart investigates a new and controversial energy rush for the natural gas found deep underground. Sometimes, this is right under the places people live in. Getting it out of the ground involves hydraulic fracturing - or fracking.Iain travels to America to find to find out what it is, why it is a potential game changer and what we can learn from the US experience. He meets some of the people who have become rich from fracking as well as the communities worried about the risks.