James Blish 
Vor 

The glowing ovoid plummeted downward, the whole sky screaming like a metallic banshee as the air boiled away from its sides.A supersonic bang broke over the forest, but the thing was already gliding down to Earth. As the ovoid settled in among the trees, the entire forest burst into flames.A thin black line appeared and etched a perfect circle on the side of the metal egg, then thickened into a door. The air was rent by a searing hiss. Slowly, the strange being – soon to be known to all mankind as VOR – began to emerge . . .