Devil May Cry is the next book in the Dark-Hunter series. It centers around ex-god turned Dark-Hunter Sin and Katra, one of the kori of Artemis. Katra is sent by Artemis to keep an eye on Sin, to make sure he doesn't try to kill Artemis. Many years ago Artemis took Sin's powers and he only lived because Archeron tuned him into a Dark-Hunter.
There are many major reveals in Devil May Cry about Artemis, Acheron, Kat, Sin, and Apollymi. Sin, who is fighting the lethal gallu demons when he meets Kat, mistakes her for Artemis. Sin has sworn to kill Artemis for years for stealing his powers. Kat only convinces Sin that she isn't when Artemis shows up in Sin's apartment. Kat saves Sin and convinces him to let her help battle the gallu demons. She even brings in Simi and her sister, since they love to eat gallu demons.
I had seen on different blogs that most people feel that Devil May Cry makes them no longer like Acheron. I personally like him even more now than before. He has some experiences in Devil May Cry that almost make him seem human. Acheron learns a secret that had been kept from him for years and rolls with it rather than killing anyone. He has grown so much from when he lashed out at Nick for being with Simi.