Arena

The Enterprise arrives at the outpost on Cestus III to find it in ruins, and the landing party is ambushed by the unseen attackers. Kirk gives chase into unexplored space, until both ships are halted by the Metrons, an advanced race who object to the violence near their territory. They transport Kirk and the enemy captain, a reptilian Gorn, to a barren world to fight alone. The loser's ship will be destroyed. The Gorn is far stronger, but Kirk finds the raw materials for gunpowder and builds a crude cannon loaded with diamonds. Having learned that the Gorn regarded Cestus III as an intrusion into their space, Kirk wounds his opponent but refuses to kill him. Impressed by this mercy, the Metrons spare both crews and return the Enterprise far away, suggesting humanity may be worth meeting again in a few thousand years.