Witch's Wake is set in a unique setting created specially for the module, which features a dark, mysterious world and lots of unique sub-races with their own special bonuses.
The game starts as the player character awakens on a battlefield with all his/her memories lost. A dying prince asks him/her to deliver to his father a message that "she is dead". Soon, the PC meets Night Hag, a witch that is very willing to help him/her discover his/her past. She grants the PC passage to the Plane of Sorrow - a place where the living world collides with the world of the dead, Stygia. The Plane of Sorrow is inhabited by the souls who are about to enter the world of undead, and Filchers, the spirits who is notorious for their thieving nature. The player journeys through the world of the game looking for answers and an only man who is left from the PC's squad, sometimes visiting the Plane of Sorrow. After venturing through some dangerous encounters, the player enters dwarfs village, Brogan's Arm. Here, he/she discovers that the man he/she is looking for has stolen the Cavanaugh Stone, a holy artifact of great importance. In the end of module, the player finally discovers the man, Caldrian, who finally reveals what happened.
The encounter with Caldrian leads the player to the realization that they were part of a Witch hunter squad who battled a witch and apparently killed her. The squad was, however, obliterated by her power, and the few survivors lost their memory. Just after the dialogue, a ghostly figure of a woman appears, writing a message "The fields of battle lie in the hearts of men...".
At this moment, the story ends with the player discovering the truth of what happened to him and his squad. A prompt to begin the next installment of the module appears, but since the sequel was never finished, this option does nothing.
Source: Wikipedia, "Neverwinter Nights: Witch's Wake", available under the CC-BY-SA License.