On this page of the Biomutant game guide, you will find a detailed walkthrough of the main story quest Out-Of-Date.
Out-Of-Date is always happy to help - go to the Tree of Life and talk to him about his big plan.
Return to Out-Of-Date
You will meet Out-Of-Date in the cave under the Tree of Life. The entrance there is in the place marked in the picture above.
During the conversation, you will learn that the Out-Of-Date fears that the end of the world could still happen, so he prepared for the worst and created The Ark. There is room for 4 more people in the Ark, and you have to decide who deserves it.
Once you have completed all the tasks for a particular NPC, you will be able to offer them a place in the Ark. Choose wisely because once you give your word, you cannot take it back. Also note that depending on your character's aura, some characters may decline your invitation.