A second background installment in the Sime/Gen series (cf. Lichtenberg's House of Zeor novels and the Lorrah/Lichtenberg First Channel)--with the human race mutated into Gens, who secrete ""selyn,"" and Simes, who must obtain selyn to survive. Initially the relationship was parasitic, entailing the painful demise of the terrified Con donor; thus Simes and Gens co-existed in fear and hatred. But now Sime ""channels,"" who can extract and transfer selyn without harming the donor Gen, are struggling to build a peaceful, stable, mutually dependent society. And young Zeth, entering Simehood, becomes a talented channel--but his path to maturity is fraught with perils: the resentment of his Gen friend Owen, who lost an arm through Zeth's irresponsibility; the mysterious morbid illness of his channel father Rimon; the threats from roving bands of killer Simes (who regard Gens as cattle) and government tax collectors; and the hostility of Gen religious leader Maddok Bron, to whom Simes are demon-possessed. As before, then, the Sime/Gen premise generates a flow of ingenious (if uneven) ideas and an appealing narrative (though the second half here turns predictable and more than a touch soap operatic). And, if not as intense or original as the Zeor books, this often-absorbing ""prequel"" will be far more accessible to readers new to Sime/Gen territory.