Threshold is a space habitat between the orbits of Mars and Jupiter with a population of a quarter million. Run by a latter-day United Nations, one of its duties is to keep humans off of Earth, now a preserve. Thousands of Muslim pilgrims from other systems are not pleased at being kept from Mecca. Their leader's daughter decides to experience Threshold's decadent (to her) society with the heir to a powerful exploration corporation, who is also smuggling illegal life forms into the habitat, thus threatening the stability of a conference on the rights of nonhuman races and ALIs--Artificial Living Individuals which the Muslims treat as they do their women: like property. Captain Joseph South, on a test flight through interstellar spongespace, is translated 500 years into our future to arrive at Threshold just as all this is occurring. He has strange memories of a fly-by of system X-3, which match up with visions from an artifact brought to Threshold by a prospector. The authors ( Outpassage ) tie up the other plots nicely, but leave aliens on X-3 to lead in to the next books in their trilogy.
– Publishers Weekly