Every summer, the Queen of the Night flower blooms in the Arizona desert—a sacred event commemorated throughout the Tohono O'odham Nation. But this year, one couple's celebration is prematurely destroyed by gunfire . . . and the sole witness to the carnage is a little girl who has lost the only family she's ever known. Dr. Lani Walker recognizes the trauma of her own childhood reflected in her devastated young patient. Joining Dan Pardee—a member of the unorthodox Shadow Wolves border patrol—Lani vows to keep the child safe while tracking down a ruthless killer. Meanwhile, Lani's adoptive father, retired homicide detective Brandon Walker, sees a break in his investigation of the long unsolved murder of an Arizona State University coed—while his wife, Diana Ladd, relives terrible memories of a man whose death haunts her still.