Prince of Lies, by James Lowder, is the fourth book of the Avatar series.
Revenge of a God.
The Time of Troubles is at an end, and the gods have been restored to their rightful places.
The soul of Kelemvor Lyonsbane, former lover of the goddess of magic, remains hidden from the mad god Cyric.
The will of one such as Cyric, when bent on revenge, is not so easily thwarted.