Horton's elegiac anthology of 15 mostly hard SF stories illuminates a broad spectrum of grief over love thwarted through time, space, human frailty or alien intervention, from the gentle melancholy of Michael Swanwick's "Triceratops Summer," which posits tame Technicolored time-warped dinosaurs in Vermont, to newcomer Leah Bobet's "Bliss," an agonizing riff on near-future drug addiction. Several selections address current political-social issues,...