In this encounter you'll meet the four horsemen of the post apocalypse: Death, Famine, Pestilence, and War. If you're playing version 1.27, then the four horsemen will talk and that's it. You can attack them if you want, but it's not very productive.

If you're playing an earlier version of the game, then this encounter will take the squad member who has the lowest charisma and turn him or her into the leader of your squad, effectively swapping places with your character. If you want to reverse this switch, then you'll need to give your character drugs to reduce his or her charisma (an addicition to mentats does this) and then re-visit the encounter.