Alsara: Requiem and Revolution
Isolde was the last living member of the Harith bloodline that was seeking the Keys for which the Hariths are known. If her story is to be believed, and brought to its final conclusion, then she died at the hands of strange men who threw her in a cell and never opened it again. She kept a journal, which revealed the final location of the Harith Key, but was locked shut with the power of her own blood. Apparently this deterrent wasn’t enough to keep her alive.
This journal was eventually recovered by Aslan, over a hundred years later. Because of the blood he and Isolde shared, he could open the book and read the contents; at least with some difficulty.