Butler is one of those accomplished science-fiction writers (Mind of My Mind, Survivor) who tap out their tales so fast and fine and clear that it's impossible to stop reading at any point. And this time the appeal should reach far beyond a sci-fi audience--because the alien planet here is the antebellum South, as seen through the horrified eyes of Dana, a 20th-century black woman who time-travels in expeditious Butler fashion: ""The house, the books, everything vanished. Suddenly I was outdoors on the ground beneath trees"" . . . in 1819 Maryland. Dana has been ""called"" by her white ancestor, Rufus--on her first visit, Rufus is a small child, son of a sour slaveowner--and she'll be transported back to Maryland (twice with her white husband Kevin) to rescue Rufus from death again and again. As Rufus ages (the Maryland years amount to hours and days in 1976 time), the relationship between him and Dana takes on some terrifying dimensions: Rufus simply cannot show the humanity Dana tries to call forth; Dana, drawn into the life of slaves with its humiliation and atrocities, treads carefully, trying to effect some changes, but too often she returns beaten and maimed to her own century. And most frightening is the thought that, in the ""stronger, sharper realities"" of Rufus' time, Dana is ""losing my place here in my own time."" At one point Kevin and Dana lose one another (Kevin returns haggard, after five years working to help escaped slaves), but finally Dana, fighting off complete possession by Rufus, kills him and that past forever--but not the memories. There is tremendous ironic power in Butler's vision of the old South in science-fiction terms--capriciously dangerous aliens, oppressed races, and a supra-fevered reality; and that irony opens the much-lamented nightmare of slavery to a fresh, vivid attack--in this searing, caustic examination of bizarre and alien practices on the third planet from the sun.