He was to spent his sentence in a prison located somewhere in space. He dreaded spending a decade rotting in a cell. When the spacecraft transporting him had an emergency landing to a hospitable planet, Zeno escaped into the wilderness. He was determined to live alone in a forest, there where the law could not touch him.
Unknown to Zeno the planet WAS his prison. The emergency landing was staged. The authorities of his time thought it more humane to let prisoners believe themselves to be free. They paed their debts by enduring a decade of loneliness and self-preservation anyway.