Kirk is forced to fight the captain of a Gorn vessel in single combat, with a whole sector as the prize.
After a Gorn attack destroys a Federation outpost, the Enterprise pursues the ship across space until both vessels are stopped by powerful aliens, the Metrons. They decide to settle the dispute by forcing Kirk and the Gorn captain to fight to the death on a barren planet.
The fight between Kirk and the reptilian Gorn is among the most famous scenes in the series. Kirk must improvise a weapon from the materials he finds. The story ends with a lesson about mercy, and the Gorn later returned in other Trek stories.