Strained and overcomplicated science fiction from the author of Converts (1984). A distant planet's habitable zone consists of a single vast river valley; the river itself is divided down the middle by the ""black current,"" a mysterious organic entity that may or may not be sentient. On the east bank, women sailors have linked with various scattered communities in a trading network. (The black current permits only females to sail on the river; males venturing forth more than once are driven mad and die.) Soon after young Yaleen takes to the river, her impetuous brother Capsi decides to explore the unknown west bank--by swimming beneath the black current in a diving suit. He discovers an oppressive, patriarchal society that utterly shuns the river--and then is captured, tortured, and burned alive for his pains. Later, Yaleen frustrates a plot by some river women to drug the black current; she falls into the current--she discovers it's not only alive but curious--and emerges on the west bank. In due course she's captured and interrogated, then escapes--after spilling the beans about the drug. Soon, drugged by the westerners, the black current contracts into its lair; now able to cross the river, the westerners promptly invade the east; meanwhile Yaleen is charged with contacting the black monster in the hope of sorting everything out. (The monster turns out to be the repository of the souls of the dead--with some sort of cosmic connection to far Earth--and, growing in awareness, it's decided that it wants to be a god.) A colorful, vigorous, and well-paced narrative; but artificial, with too many unlikely and unconvincing notions. All in all, a construction that's not sturdy enough to sustain all the cosmic complications.