Once on the island, Antonio colludes with Sebastian to murder King Alonso and Gonzalo. Having plotted the banishment of his brother, Prospero, twelve years earlier, he has only grown more evil in the intervening years. Antonio successfully plants the seed of murder in Sebastian's mind by appealing to his greed for power. Very cleverly, Antonio reminds Sebastian how simple it was for him to take the dukedom away from his brother years earlier and how simple it will be for him to do the same. Just as the two men raise their swords to take the lives of the sleeping Gonzalo and Alonso, Ariel awakens Gonzalo with a warning.
Their plot foiled for the time being, Antonio and Sebastian remain intent on following through at the next opportunity. When confronted by Ariel for his evil overthrow of Prospero, Antonio is unmoved. When confronted and forgiven at the end by Prospero, Antonio remains unrepentant. There is no indication that Antonio changes his ways in the course of the play.