The Saurians, a monsterous-looking group of aliens, have landed aboard the Searcher under the guise of friendship. Using a device to make them appear human, they plan to infiltrate the ship to cause a galactic war. However, Buck, who has just overcome a flu-like virus, sees the aliens for what they are. He tries to convince the crew that monsters are aboard, but to no avail. His friends believe him to be mentally unbalanced from the sickness. The Saurians fear that Buck will expose them and decide to kill the pilot before others become suspicious.