Alpha and Omega by Patricia Briggs
Alpha and Omega #0
Anna, four years a werewolf, raped, beaten, half-starved and handed from one male to another, places a call from Chicago to the wilds of Montana. She reaches the Marrok, North America's werewolf ruler, telling him she's seen a boy, one reported missing and possibly injured. He was in a cage her pack's Alpha keeps for confining new werewolves.
The Marrok says that his enforcer is flying from Montana to O'Hare. Anna meets the plane, and, Charles, enforcer, as well as the Marrok's oldest son, insists on staying with her. He has seen she is not the Submissive she thinks she is. Charles is a supreme Alpha, and she is his antithesis, a rare Omega; her very presence lowers tension, calms and soothes. Despite centuries as a Solitary, Charles would wed young Anna. His brother wolf, he says, has already taken her as his mate.
There are, as investigation and confrontation reveal, reasons both for the capture of the boy and for what has been done to Anna. It's a surprisingly tender story.