"Mom always says the angels walk among us. She forgot to tell me that sometimes they're not all fluffy and nice." Seventeen-year-old Caleb Wood has seen people he calls the walkers since he was a baby. It didn't take long for him to realize something...no one can see these strangers but him. They never stuck around or tried to touch him. And they never said a word. That was until one day on the first day of class in his senior year when an incredibly gorgeous girl strolls into his life...and things are never the same again. Soon Caleb realizes he has stepped into the middle of a growing conflict between two ancient groups. And his ability to see the invisible ones, the half-breeds that want to modify the human race, just might be the only hope both he and the mysterious, but infuriating, Gia, have of making it out alive.