The Horta
Janos Prohaska

Chief Engineer Vandeberg
Ken Lynch

Security Chief
Lt. Commander Giotto
Barry Russo

Ed Appel
Brad Weston

Schmitter
Biff Elliot

The Enterprise is called in to help investigate the deaths of some men working the deep Pergium mines on Janus VI. Kirk meets with the miners' leader, Chief Engineer Vanderberg, who explains that three months previously they had opened up some new levels in the mines that contained particularly rich deposits. Since then, fifty men had been killed and their machinery had started to corrode and disintegrate.

Nothing had been left of the men, except for some charring, and the deaths had been occurring at increasingly higher levels, now nearing the miners' living quarters. The Chief Processing Engineer claims to have seen the creature responsible, which he describes as 'big and shaggy' and which seemed to be immune to the type 1 phaser he had fired at it. Spock enquires about a large silicon sphere in the office and is told that the miners have found and destroyed thousands of the nodules in the new levels.

McCoy examines the remains of the latest victim, a man called Schmitter, and finds that his body was corroded away by a powerful acid-like substance. Spock maps the attack pattern and concludes that the creature must be able to move incredibly fast, but a sensor scan shows no life signs in the deserted mines. Another attack occurs and a critical part is stolen from the colony's main reactor without which it will go critical in 48 hours. This convinces Spock that the creature must be intelligent and he suggests that it may be silicon-based. He says that his would explain why the ship's sensors failed to pick it up and that their type 2 phasers should be set to compensate.

Security teams are brought in to search the tunnels and, after one of their crewmembers is killed, Kirk and Spock track the creature through a freshly cut tunnel. Only one creature can be detected although, due to the large number of tunnels, Spock believes that there must once have been many. The creature appears and they hit it with phaser fire before it escapes down the tunnel. With the reactor due to fail imminently, the Enterprise starts to evacuate non-essential mining personnel but Vanderberg and some of the more vengeful miners remain behind.

Kirk and Spock separate when the tunnel branches and Kirk discovers a cavern full of the silicon spheres which Spock, on being informed, advises him not to damage. The creature appears before Kirk, causing a cave-in that cuts them off. Kirk aims his phaser at it and notes that this persuades the creature to back off. Spock calls on his communicator and urges Kirk to kill it but he decides against it, preferring to wait for Spock to make his way through to them.

In the meantime, the creature displays its phaser-induced injuries to Kirk. On arrival, Spock attempts to mind-meld with the creature and discovers that it is called a Horta. It is in such pain from its wounds that he is forced to break contact, following which the creature uses its acid to burn the words 'NO KILL I' into the rock floor. McCoy is summoned to try and help it, complaining that he is a doctor, not a bricklayer. Spock tries another mind-meld, this time physically touching the creature.

Now able to block out the pain, he discovers that the Horta is the last of its kind and that the silicon spheres are its eggs, which it is protecting. The Horta agrees to return the stolen reactor pump and leave the miners alone as long as its remaining eggs are left untouched. McCoy manages to patch up its wounds with thermo-concrete and everyone ends up happy. By the time the Enterprise leaves orbit the baby Horta have begun to hatch, digging tunnels everywhere and leading the miners to untold riches.