A dull murmur, like distant thunder, reached their ears and brought Biggles to his feet with a rush. 'What is it?' he gasped.-At the first sound Dickpa had leapt for the flashlight. 'Quick,' he snapped, as the floor of the cave sagged sickeningly. 'Get out - it's an earthquake! Ah - stop!' he screamed. A visit to Biggles' uncle, Dickpa, lands Biggles, Algy and mechanic Smyth in a dangerous adventure looking for an ancient Inca treasure hoard.