The Enterprise is on a mission to transport the pet waoul of the Moauvian ambassador from Centarus Base back to his homeworld of Moauv. Moauv is neutral, but it lies near both the Klingon and Romulan neutral zones. Moauvians are an advanced, logical people. The ambassador’s pet is called a waoul and it looks like a cross between a nervous bobcat and a furry lizard.
While hunting down the animal aboard ship, the crew’s voices start yowling and later fights break out among them. Any person who comes near the animal starts feeling the need to get away and hide and begin to see things through the waoul’s perspective. The situation grows serious as the crew starts wanting to strike out and run in blind panic. Spock determines that this effect is a result of a mass telepathic projection from the terrified animal.
To prevent the ship from being disabled by the telepathic effect, Kirk contacts Moauvian Ambassador Oavid. Oavid tells Kirk that his people do not know how to capture a frightened waoul either. Kirk and Spock personally go to look for the waoul in a corridor and soon start fighting because the animal comes near. Relief communications officer Lieutenant M’Ress shows up and takes care of the waoul, which stops being scared when she picks it up. The crew contacts the Moauvian ambassador and tells them that they found the pet. Ambassador Oavid tells the Enterprise crew that his pet waoul is a female and is expecting kittens.