Three years later a second mission, M-2, lands with a crew of four consisting of Major Merritt, Captains Buckley and Lazzari and Lieutenant Johnson.
Major Merritt, the leader of the expedition, was asleep when Captain Buckley exited, but goes out to find him and becomes trapped on a rock when the Sand-Beast pursues him.
"The episode was based on a short story by Jerry Sohl, 'The Invisible Enemy', which was first published in Imaginative Tales magazine in September 1955.
After a ten-man expeditionary team is consumed from inside a forcefield, the ship's computer suggests, unconvincingly, that "invisible" birds are to blame.
Lazzari kills himself by smashing his head against a bulkhead and the remaining crew gather outside the ship to give him a military burial.
Allison watches helplessly as the funeral party is eaten by "large, heavy, porpoiselike creatures ...swimming up out of the sand as if it were water.
"[1] After reading Sohl's first draft based on his short story, ABC decided the monster should appear sooner, so Seeleg Lester rewrote the script.
After further rewrites by Sohl, the script was passed to producer Ben Brady, who rewrote the last act into a "calm fourth quarter".