Time has run out. Physicist David Keith has spent the past 30 years fighting for research into a disruptive, planetary-cooling technology called solar geoengineering. He knows for certain it will work, it’s fast, and in the words of Al Gore it is “utterly mad”. Defiant in the face of personal attacks and death threats, his attempt to launch the first experiment into the stratosphere has divided the environmental community, spawned the viral chemtrail conspiracy and inspired a rogue start-up company to begin their own deployment. As he drives this idea out of the lab and into a planet in the grips of a climate meltdown, are there any ideas too risky to explore?