Once there was a civilization of fish. It was not a bad life really. Swimming came naturally.
The watery environment supplied all that was necessary to fishness and the fish adapted to the temperature of their world. There were big fish and little fish, fat fish and skinny fish, good fish and bad fish. They were generally busy with survival, but survival was not impossible and it was all they had ever known. They gathered in schools and learned from each other about being fish. They had fish meetings, lived in fish families, planned fish careers.
Life as a fish did have it's risks. The only way to grow was to eat other, smaller fish, which was a serious drawback as long as you were little, but became easier the bigger you got. The large and wise old fish felt it was equitable and the small, young fish didn't get to vote. There were no small old fish.
Occasionally, certain fish of a particular sort would speak about what they called "Life Above". You see, the fish universe stopped at a clearly marked border overhead, known as the Eternal Plane. No one knew for sure what it was or how it had arrived, but it had always been there and above that point it was known that no fish could survive. Sometimes fish died of natural causes and floated upward to this plane where they just drifted away. The whole situation presented the fish world with a perplexing question -- what's up there?
The ones who spoke of these issues held that there was some form of life "up there" which was larger and more powerful, somehow more "real". They taught that there was a whole world out of reach to fish in there natural state, inhabited by creatures radically different from anything the fish had ever known. It was said (mostly by rather different fish who claimed to understand) that someday all fish would be drawn through the Eternal Plane and have to answer for all there fish-deeds to Someone in that other world. In order to prepare for this answering these fish recommended some sort of religious conversion.
These thoughts were added to by personal stories of some who had had the "out of water experience". This could be achieved by starting deep and rushing headlong to the edge of the universe, momentarily breaking through and then re-entering life again. No scientific knowledge could be developed in this field of study, however, because the experimenters would either return quickly or simply disappear forever. And those who did return were confused and unable to adequately describe what they had seen.
But most fish didn't believe or even have time to think about such things. They had places to swim, things to do, others to eat. Life was more than full.
The fish universe burbled along for many millennia. In every generation there were those who took the "life above" seriously and swam in a way which reflected their conviction. They became known as the "good ones", but it was not a complement. The vast majority of fish were committed to other ways of understanding their universe, ways which made more room for what they wanted to do and think.
Then one day the unthinkable happened. The fish universe began to close in. There were great ripples in the Eternal Plane overhead and then a terrifying, crushing togetherness. The fish swam furiously against the inexorable pressure, but to no avail. Some overwhelming power was lifting them toward the Eternal Plane. It all happened so fast. There were so many unfinished fish tasks, so many unsung fish songs, so many dashed fish hopes. All gone.
In the other world the fish were separated into two groups -- good fish and bad fish. This was quite infuriating to the bad fish (much the larger group) because they had always thought of themselves as really good at heart, though they had violently rejected the concept of ultimate goodness. And they thought it was unfair and wrong that they should be all piled together as if there were no other distinctions. After all, even among the bad fish, there were some who were worse than others, and the somewhat good ones bitterly resented being classed with the much worse ones. They wanted a chance to argue with the mighty creatures who handled them, but lacked the capacity to understand or communicate. And there was a strange sound in the distance. Something they had never heard before -- a furnace.