The game is about three people who are known mostly by their nicknames. Two men Bachelor (Бакалавр) and Haruspex (Гаруспик), and a girl nicknamed Devotress (Самозванка). Each of whom tries to uncover the source of a strange lethal sickness that befalls a small town. Although you can play as each of them, there is only one storyline, which is seen from different points of view depending upon the chosen character. Some of the secrets can be uncovered only by the consecutive playing of each character. Every day you receive quests from NPCs and at exactly midnight of each day, the incomplete quests are erased from your notebook. Quests are divided into main missions (one per day, which decide if a major character will die), and side quests to complete to earn money and items.
On the edge of town, there is a great building named Polyhedron (Многогранник), an impossible geometric structure used as a fortress by children. On the opposite side, a great ominous mountain called the Abattoir, with the Apiary, an insane asylum, next to it. All districts and major buildings of the town are named after body parts and biology.
Source: Wikipedia, "Pathologic," available under the CC-BY-SA License.