For better understanding, The Corner Stone was written as a back story for many characters involved in Hallowsted. It isn't a chapter on its own, more of a spin off. The Corner Stone could be a book on its own. It is only the beginning. The whole reason it was introduced was to barley touch upon Hallowsted,s curse. How exactly? Who is Iris?
Btw, if you didn't realize, the drake Edmond is given is Gaunt.