While Tom Swift is working on his latest new invention, the electric rifle, he meets an African safari master whose stories of animal-hunting sends the group off to deepest, darkest Africa!  They find out some old friends are being held hostage by the fearsome tribes of the red pygmies.

Swift invents the electric rifle, a gun which fires bolts of electricity. The electric rifle can be calibrated to different levels of range, intensity and lethality; it can shoot through solid walls without leaving a hole, and is powerful enough to kill a rampaging whale, as in their steamer trek to Africa. With the electric rifle, Tom and friends will have to bring down elephants, rhinoceroses, and buffalo, and save their lives in pitched battle with the red pygmies.