Shattered Soul and Weakened Wings

AU where angels are sold as slaves. Sam and Dean aren't hunters. Dean Winchester buys Castiel, an abused angel, in hopes of saving him from slavery. Unfortunately, Castiel isn't used to nice treatment. What will it take for him to believe Dean when he says he's no longer a slave? Fluff, torture, accidents, cuddles and crying. Destiel. Sabriel. Rated T for physical and sexual abuse.