The protagonist has had his sense of pain rewired so he instead merely sees flashes of light. He has been sent out on an endless journey to explore potentially habitable worlds. The story begins after he has been at it for some indefinite period of time, experiencing tortures of all kinds--and not caring, since he can feel no pain. The signal to return to Earth, long awaited, has not come.
He cannot tolerate the interminable journey any longer, and begins injuring himself--gruesomely--to force his automated scout ship to retrieve him from the planets. Eventually, he is rescued by a group of traveling empaths. They cannot tolerate pain, so he is the perfect companion for them, able to go down to planets and collect exciting new foods, and live a life of total hedonism.
However, this lifestyle--not so different from his previous one--is also intolerable to him, so he convinces them to take him to Earth. When he arrives, he discovers just what his pain receptors have been rewired to:
He decides to stay on Earth--however briefly he might survive--despite the unbearable pain, since it is real.
|James Tiptree, Jr.||Author|