Loomis finds himself in Caul, The Library of Ages. Being a Hemihence, a soul unable to leave until he can forget, or be consumed by memories from his previous existence, and so becoming a Crowling, A servant to Raziel, The Angel of Secrets.
There he meets Angus, a Hemihence That's being used by a mad soultamer named Metreaus to find Raziel's Book of Secrets and ultimately The Tablets of Destiny. If Loomis doesn't help Angus escape Metreaus, he will be lost forever, body and soul.
In a world of vestigial plots and reminiscent traces of past lives, Loomis must confront his past, in order to help Angus before Metreaus consumes his soul and unleashes into the universe and ancient darkness.