Australia’s strict quarantine rules have been breached and an alien strain of Dermatobia hominis, the human botfly, has crossed with the harmless native variety, creating a new and deadly strain which flourishes with all the vigour of an introduced species.

Adam Wilde’s father is searching for a variety of botfly safe to humans and genetically dominant to the deadly Variant X. On board the Carlotta, a floating laboratory on a tributary of the Amazon, he works with his wife and son in cooperation with the local Indians.

Adam’s tranquil existence on board Carlotta is disturbed by the arrival of an old friend and colleague of his parents. Jerry Loundes has come to help and has brought his fourteen-year-old daughter Sharma with him. Adam resents Sharma’s intrusion and she, in turn, is hostile towards Adam and his family.

In the heat and humidity of the forest, tension builds to breaking point and things start to go very, very wrong.