Venusian lullaby

"You want me to help you eat your children?" Ian said. Jellenhut's eye-stalks twitched. "How else would we remember them?" Venus is dying. When the Doctor, Barbara and Ian arrive they find an ancient and utterly alien civilization on the verge of oblivion. War is brewing between those who are determined to accept death, and those desperate for salvation whatever the cost. Then a spacefaring race arrives, offering to rescue the Venusians by moving them all to Earth—three billion years before mankind is due to evolve. Are the newcomers' motives as pure as they appear? And will the Doctor allow them to save his oldest friends by sacrificing the future of humanity?