He must enter the innermost cave where he will challenge and defeat Medusa using the shield made for him by the hunters. When he leaves the cave with the head of Medusa, the elixir, he meets Io. Calibos returns and is defeated by Perseus who was forced to use the sword given to him by Zeus, a sign that he is beginning to recognize his true self. Perseus is once again faced with the choice of whether to continue his journey or stay with Io who is dying. Luckily for Argos, that choice was made for him when Io turns into a yellow mist and vanishes