The first space flight to Venus returns to Earth carrying a specimen of Venusian life called the Ymir. When the ship crashes into the sea upon its re-entry into Earth's atmosphere, the small, reptilian creature escapes, growing to an enormous size, eventually terrorizing the city of Rome. The always beautiful and impressive creature animations of the great Ray Harryhausen elevate the film above the level of ordinary 1950's monster sci-fi. The Ymir is one of the best-known creations in his long, distinguished career.