There is a creature called Narghile that produces a pellet that erases human memories. Rorty and Muriel vows to get rid of these creatures by launching them into the sun. Muriel ends up dying and Aeon, out of guilt, takes her place as Rorty and her try to finish it out. Rorty finds out (from Aeon) that Muriel was cheating on him with Trevor, which he doesn't believe at first. He gets proof himself and can't deal with it. So, he takes the pellet erasing all of his human memories about Aeon, the pellet and Muriel. (thetvdb.com)