Unicorns roam the uplands of Libby Quarrels' mountain ranch. When Libby takes the AIDS-afflicted Bo Gavin out of exile in Atlanta to live with her in Colorado, she sees no connection between his disease and the fantastic secret she guards. But it so happens the unicorns suffer from an ugly, implacable plague of their own, and the parallel world that touches the high country has unleashed magic sinister as well as marvelous. While Libby's Indian ranch hand Sam is stalked by his wife's headless ghost, his estranged daughter has visions that propel her toward the grueling Sun Dance ritual, where an encounter with the spirit world may decide the fate of both the unicorns and the people whose lives they've touched.