In the story's world-line there exists a magical realm beneath the surface of all things—referred to as the Twilight (or Gloom in other translations). The action in the novel centers on a group of people referred to as the Others—human beings who tapped into the Twilight and gained super-normal abilities. The Others were the humans (shamans, soothsayers, and wise men) from long ago who figured out how to step into the Twilight. However, the Others are different from humans, they are born as Others. Humans are not able (at least in the first part of the tetralogy) to become Others. The Twilight does not offer its gifts freely; it feeds off the strength of those Others who enter it. If sufficiently weakened, they are consumed, never to return to the ordinary world. The aura of any Other, or emotional state at the time of their first entry into the Twilight, determines whether or not the Other will become a 'Light' or 'Dark' Other. Furthermore, once determined either Light or Dark, an Other must choose what specific powers they will borrow from the Twilight. Variations such as vampires, magicians, and healers are all possible, each with their own benefits and restrictions. Often, the choice is made by the state of mind but if choosing Light or Dark during Initiation, a Watch can attempt to steer the powers of someone into what they need at the time. "Initiation" refers to the process of an Other choosing not Light or Dark but choosing to officially be a part of the Night Watch (Light Others) or Day Watch (Dark Others). An Other can exist without being initiated as part of a Watch, still independently capable of entering the Twilight and becoming Light or Dark. The choice of becoming light or dark, even what specific powers you gain is usually final.
The division of Light and Dark had always existed between the Others. Those of the Light believed it was their duty to help the weak and the helpless. Those of the Dark shunned all obligations. They did what they wanted, regardless of morals and consequences. For many millennia, the two sides fought a vicious battle. Both were willing to use any means necessary to achieve victory. Eventually they realized that if they continued their battle, neither side would survive. The leaders of both sides forged the Grand Treaty—a set of laws to govern the way the Others used their powers. The Light Others created the Night Watch, the Dark Others the Day Watch, to ensure that neither side would violate the Treaty. The Inquisition, a group composed of both Dark and Light Others, was created to arbitrate.
If they spend them too quickly, the Others can use the feelings and emotions of the humans surrounding them to recharge their powers. The Dark Others use negative emotions such as pain or anger, the Light Others use positive emotions such as joy. Feeding on pain causes pain to increase, feeding on joy causes joy to wane. Because negative emotions are much easier to achieve in humans, this arrangement creates a situation where the powers of the Dark Others are easier to recharge and are much more readily available than those of the Light Others.
Since the signing of the Treaty, the Night Watch and the Day Watch have kept their eyes on each other, diligently policing every violation. The old leaders continue to plot, using humanity and the Others as their pawns. Only time will tell which side will prevail.
Anyone else read this book series?