Gentle Giants of Ganymede

Long before the world of the Ganymeans blew apart, millennia ago, the strange race of giants had vanished. All that remained of them was a wrecked ship, abandoned on a frozen moon of Jupiter. Now Earth's scientists were there, determined to ferret out the secret of the lost race. Then suddenly the Ganymeans returned, bringing with them answers that would alter all Mankind's knowledge of human origins . . .