A heatwave is welcome news for many; but as temperatures continue to rise, the effect on Earth is devastating - earthquakes, floods and droughts place countless lives in danger. International Rescue is stretched to the limit by the demand for its services, and Jeff tells Brains to discover the reason behind the freak weather. The source is the overheating Sun, which Brains deduces is about to expel a piece of debris so large that it will form a new planet. Only International Rescue can react fast enough to avert a global disaster. Thunderbird 3 is launched and Operation Sunburst begins...