30 parts Complete Prince Castiel of Paradina has always followed his father's orders, and he's always wanted to protect his people, which is why he didn't argue when his father told him he would be escorting his sister Hannah to the kingdom across the lake for her to marry Prince Dean of Terren. Hannah is nervous, and so is Castiel, but Sam and Dean Winchester and their friends help put the two of them at ease.
But not long after their arrival, an attempt is made on Hannah's life. It is unsuccessful, but the entire castle is now on guard, and Castiel must find out who would want his sister dead and why... all the while dealing with the feelings that are emerging for Dean Winchester.
(So in addition to this being an arranged marriage AU, this is also a wings AU, meaning Cas and his family have wings. Just so you weren't blindsided by that.)