The Devil in the Dark

The pergium mining colony on Janus VI calls in the Enterprise after dozens of miners are killed, burned by something that tunnels through solid rock. The creature also steals a vital part of the colony's reactor. Kirk, Spock and a security team hunt it through the mines with phasers set to kill, and Kirk wounds it. Spock notes that it may be the last of its kind and urges caution. Cornered by the creature, Kirk realises it does not want to harm him, and Spock makes a mind meld. It is a Horta, a silicon-based mother whose thousands of eggs the miners have been unknowingly destroying. McCoy, protesting that he is a doctor, not a bricklayer, patches her wound. The miners agree to a truce: the hatching young Horta will tunnel for minerals, and humans and Horta will share the riches of Janus VI.