In the story's worldline, 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 supernatural abilities.

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.

An Other can exist without being initiated as part of a Watch, still independently capable of entering the Twilight and becoming Light or Dark.

Except for the prologues, the majority of the events in each story are written in a first person narrative using the voice of the Light Magician character Anton Gorodetsky, a member of the Night Watch.

A Mage, recently reassigned to field work in the Night Watch, Anton Gorodetsky, is tasked with tracking vampires who have been hunting and killing humans without a licence.

He finds the vampires who have been calling Egor, and in the struggle to arrest them, because he has used up the amulet trying to do good elsewhere, is forced to kill one while the other (a female) gets away.

As events unfold he discovers that Olga can speak and appear briefly as a human, and is a sorceress trapped in an owl's body as a punishment.

But when he does, one of the minor Light Mages, Ilya, reveals himself to be Boris, who'd swapped their bodies, and blocks Zabulon's efforts.

A Dark Other, Galina Rogova, is killed by Maxim, a mysterious murderer using an enchanted wooden dagger, referring to himself as "The Judge".

Anton, curious why the Dark Other had not returned from the toilet, briefly leaves Svetlana and discovers the body.

Anton flees, pursued by Zabulon and grabs a lift from a passing car whose driver sees the magical events as a gangland shooting.

While talking to Olga, Anton realizes that the Day Watch is only chasing him in order to make Svetlana angry and use her powers illegally, which would allow them to use the law to neutralize her as an agent of Light.

Secretly penetrating inside, he sees a bunch of incompetent Dark mages directing the search for him.

An old man arrives from Uzbekistan and is intercepted by a team of Dark Others led by Alisa, who attacks him thinking he possesses a coveted artifact.

All of the Night Watch operatives go to Tiger Cub's house to relax, but Anton doesn't manage to have fun, as he is concerned with Svetlana's growing powers influencing their relationship and the reason Gesar sent them off.

He finally leaves, and when he gets back to his apartment, he discovers Zabulon calmly reading a newspaper and waiting for him.

Zabulon reveals that Alisher, the young man from Uzbekistan, brought with him an artifact, a piece of chalk.

The Twilight, although a realm of existence beneath the human or ordinary world and therefore not sentient, indiscriminately absorbs energy from whoever enters it.

The skill required to stay (or even enter) into the Twilight for an extended period of time is acquired through formal training.

Others who lack this skill yet still manage to enter the Twilight are at an increased risk of being completely drained of their life and energy.

Zabulon takes on the form of a red, rock-skinned demon with horns and a tail, also with slits for eyes and a forked tongue.

For instance, humans can be seen but they are sepia-toned and are moving at a much slower rate due to the time difference between the two realms.

This level is inhabited by a parasite, a blue moss feeding on energy, which doesn't seem to do any harm to those who enter the Twilight, and is easy to eradicate.

There is a theory mentioned in the books that states that large colonies of dark blue moss can unbalance the human psyche and cause psychosis but it has not been proven.

Nonetheless, the protagonist of the Night Watch—Anton—occasionally feels compelled to utilize magic to burn off the blue moss at points in the story.

Night Watch mentions that the deepest levels have been navigated by Zabulon (see character descriptions below) but at the cost of great energy expenditure even to him.

When an Other dies of natural causes, is killed, or dematerialised (executed) their "soul" or "essence" is passed into the Twilight where it remains for all eternity.

In the second part of the Night Watch, what is assumed to be a dematerialised Other in the Twilight seemingly communicates with Anton as it points him towards the TV tower where the Day Watch has set up its field headquarters as it searches for Anton (who is being framed for killing Dark Others).

In 2005, Nival Interactive released the video game Night Watch, based on both the novel and film adaptation.