Joe Carstairs is a boy on a farm in Australia. His father is a keen naturalist who, some years before had set off for New Guinea in search of specimens, and never been heard of again. Joe is old enough to mount a search expedition, and takes with him a local doctor and an aboriginal worker on his farm. They find themselves joined by a stowaway, Jimmy, whose father is a squatter (farmer) nearby, together with his dog, Gyp. This team sets off, arrive in New Guinea, hire some more porters, and travel guided by some sixth sense straight to where Mr. Carstairs has been kept a prisoner, along with another Englishman, whose mind has gone, under the stress of his imprisonment.