The Doctor brings Flip to the futuristic city of Festin, the best vantage point to witness a unique astronomical light show. In a city governed by the all-powerful network known as the Cortex, they’re soon identified as outsiders – nihilists, perhaps, responsible for a wave of terror that’s been sweeping the city… But the truth is different. The people of Festin are burning up. Spontaneously combusting. And no-one knows why.