Hydrogen fueled the early combustion engine and propelled we humans to the moon. But the story doesn't end there. Scientists around the world are now bringing it back in from the cold to fight global warming. From powering public transport to producing electric vehicle batteries out of waste, hydrogen's potential for once again changing the game is huge. Together with a US public broadcaster, we meet the people ushering in an all-new, all-clean era for this most abundant of natural elements.