Alien From The Stars

Can it be that of all the billions of probably planets, revolving around strange suns, in far corners of the Universe, ours is the only home of intelligent life? If life has managed to come into being elsewhere on some bizarre, grotesque world, just how strange and alien will that life be? What if its own planet is dying? It would need a new environment, and the questing ships of its explorers would traverse the void. What if they find Earth and decide that it suits their purpose perfectly... except for man? How would the battle be fought and who would win?