TROPICAL NIGHT FALLING by Manuel Puig, translated from the Spanish by Suzanne Jill Levine (Norton: $8.95; 189 pp.). The last novel by the author of “Kiss of the Spider Woman” takes the form of an extended dialogue between Luci and Nidia, two aged Argentine sisters living in Rio de Janeiro. Like the characters in “Spider Woman,” the slightly dotty sisters live in fantasies. But their imaginations have waned with the years: Their daydreams are limited to recollections of the pleasures they once shared with their children and speculations about their neighbors, especially Silvia, the psychotherapist. Initially, their lengthy discussions of what may or may not be occurring in Silvia’s troubled romance seem to be so much idle chatter, but as the story emerges from the speculation and hints, Puig beguiles the reader with a gentle tale of love, dependence and illusion. “Tropical Night” may lack the political import of his earlier fiction, but it provides a light-hearted coda to a distinguished career.