Out here we are the only police men around, and a crime has been committedAs they are pursuing they come somewhat near to a solar system and the enemy ship stops completely. Kirk is happy that he will now be able to catch up, but the Enterprise is also stopped. They get a signal from the solar system that they are an advanced race who doesn't like the violence going on here, they decide that the best thing to do is take the two captains of the ships, let them battle it out and the winner will go free, the loser will be destroyed.
It turns out the enemy is the Gorn, they are extremely strong physically, Kirk throws some rocks at him, and even drops a boulder on him from quite high up, but he is not killed. Kirk then takes a bunch of minerals and puts them into a bamboo shoot to make a cannon of sorts. He nearly kills the Gorn but changes his mind at the last second. Leading up to the final attack by Kirk, the Gorn tells him they killed the colony because it was encroaching on their territory. Upon reflection, Kirk realizes this is a possibility because it is an unexplored area of space.
An angel looking guy shows up, he's from the nearby solar system and is supremely impressed with Kirk for not killing the Gorn. He says they are still half savage, but perhaps in a thousand years or so they can make contact with each other again.