Who was Ego before he was a Living Planet? Thor enters the dark recesses of Ego's mind…and surely wishes he hadn't.
At the request of Galactus, Thor teams up with Firelord and Hercules to battle Ego, an ancient sentient planet that destroys everything in its path. During the battle toward its "brain" Thor is absorbed into its mind and experiences first-hand the last hours of the people who used to live on this planet, before their sun had gone nova. Thor relives the memories of a scientist named Egros. To save his people he had devised "Progject Worldcore." They had tunneled to the core of the planet and made chambers where the people would sleep until the planet was livable again. But his calculations were off by fifty seconds, and before they could seal the chambers safely... their sun burst.
The blast of radiation melded the mind of Egros to the whole planet -- his life feeding off of the two billion men and women who died. For a million years his guilt threatened to drive him insane, but he didn't give in to the darkness... until Tana Nile removed a portion of his planetary surface.
Now knowing Ego's history, Thor tries to put the planet out of its misery by smiting its brain, but only succeeds in stunning it.
Galactus saves the day by attaching a propulsion unit to the southern pole of the planet and sends Ego into exile.
The issue ends with Thor talking Galactus into freeing his servant Firelord, and replacing him with the Destroyer.
Moral of the story: Don't procrastinate. If your sun is going to explode, give yourself at least an extra minute to seal your life chamber.