Preface- How Did We End Up Here?

The Hale fire left Derek with a little bit of PTSD when he sees fire. One day his new apartment went up in flames while he was still in it. Stiles came to the rescue. While recovering at stiles house a little relationship forms between them. No more bickering between them anymore. Though the question still remains. Who started the fire?"
This story involves:
-lots of sterek
-tiggers
-boyxboy
-Scisaac
- idk