The weird Dr. Atlantian rises out of the ocean near New York City in his hive-like machine, which derives its power from Lunar motion. Atlantian represents the lost continent of Atlantis, which has developed an advanced technology in its centuries of undersea existence and now intends to conquer the surface world.
While investigating the mysterious extinction of four billion inhabitants of a solar system, the Enterprise encounters NOMAD - a computer space probe which has transformed itself into a relentless exterminator of `imperfect biological specimens'.
Episode aired Feb 7, 1970
The Doctor attempts to convince people there are monsters in the caves, prompting Major Baker to start shooting at a reptile man.