In Volcano Adventure, Hal and Roger Hunt are off to the Pacific to study volcanoes with a young scientist, Dr Dan Adams They share some amazing experiences - investigating an active crater on the sea bed seeing the inside of a boiling crater in a steel and glass ball and resuing the inhabitants of the doomed 'Tin Can Island' But Dr Adams is behaving strangely and Hal begins to worry that he might be putting them all in danger In South Sea Adventure, Hal and Roger are commissioned to bring back some extraordinary sea creatures for their father's collection, but that's not their only mission They're also out to visit the remote pearl-oyster beds of a secret lagoon, but there are others after the pearls as well, and they soon find themselves stranded on a desolate atoll with little hope of survival