Biggles is summoned suddenly to the London Hospital for Tropical Diseases, where he hears the deathbed revelations of a man named Linton, who has a message from a mutual friend, Angus Mackail. Linton and Angus, alongside many others, were duped into investing in farmland reclaimed from the jungle in central South America, an area known as Paradise Valley.

But this is no second Eden. The 'investors' swiftly found themselves as little more than slaves working the land for the owner of the valley, the enigmatic and silver-tongued Dr Leibgarten. Imprisoned by the lethal jungle and desert surrounding the valley, it took a superhuman effort for Linton to escape, and costs him his life to deliver the warning.

Determined to rescue Angus and the other captives, Biggles wastes no time in getting Algy, Ginger and Bertie on the case, and takes to the skies. But they swiftly find out there is far more going on in Paradise Valley than Linton could ever have suspected...

Biggles is at it again in the fourth daring adventure in the Special Air Detective series.