The four crew members are transported to an Earth-like city filled with many cultures and must force a light source to strike a certain space on an ancient pyramid. When they accomplish the task, Kulkukan appears as the winged serpent, alleging to be their master. Transported to an ominous "life-room," the crew members notice a variety of creatures from around the galaxy, including the ferocious, but now peaceful, Capellan power-cat. Kirk explains that they cannot accept Kulkukan as their master, despite his contributions to mankind.

On the U.S.S. Enterprise, Spock discovers a way to break the energy field surrounding the ship, distracting Kulkukan from the other crewmen. The men release the animals from their cages, thereby creating a chaos which Kulkukan is unable to control. The power-cat traps Kulkukan and prepares to kill him so Kulkukan is forced to reveal himself as a mortal. Kirk saves Kulkukan and thus teaches him a valuable lesson about human survival. Kulkukan leaves as an old, broken mortal, and Kirk decides that the price of infinite knowledge is too high to pay.