Ivan Denisovich Shukhov has been sentenced to a camp in the Soviet gulag system. He was accused of becoming a spy after being captured by the Germans as a prisoner of war during World War II. He is innocent, but is sentenced to ten years in a forced labor camp.
The day begins with Shukhov waking up sick. For waking late, he is forced to clean the guardhouse, but this is minor punishment compared to others mentioned in the book. When Shukhov is finally able to leave the guardhouse, he goes to the dispensary to report his illness. Since it is late in the morning by this time, the orderly is unable to exempt any more workers, and Shukhov must work.
The rest of the novel mainly deals with Shukhov's squad (the 104th, which has 24 members), their allegiance to the squad leader, and the work that the prisoners (zeks) do: for example, working at a brutal construction site where the cold freezes the mortar used for bricklaying if not applied quickly enough. Solzhenitsyn also details the methods used by the prisoners to survive; the whole camp lives by the rule of survival of the fittest.
Tiurin, the foreman of gang 104, is strict but kind, and the squad grows to like him more as the book progresses. Though a "morose" man, Tiurin is liked because he understands the prisoners, he talks to them, and he helps them. Shukhov is one of the hardest workers in the squad and is generally well-respected. Rations at the camp are scant, but they are one of the few things that Shukhov lives for. He conserves the food that he receives and is always watchful for any item that he can hide and trade for food at a later date.
At the end of the day, Shukhov is able to provide a few special services for Tsezar (Caesar), an intellectual who is able to do office work instead of manual labor. Tsezar is most notable, however, for receiving packages of food from his family. Shukhov is able to get a small share of Tsezar's packages by standing in lines for him. Shukhov's day ends up being productive, even "almost happy": "Shukhov went to sleep fully content. He'd had many strokes of luck that day." (p. 139).
Those in the camps find everyday life extremely difficult. For example, prisoners are only exempt from outdoor labor if the thermometer reaches −41 °C (−42 °F); anything above that is considered bearable. The reader is reminded in passing, through Shukhov's matter-of-fact thoughts, of the harshness of the conditions, worsened by the inadequate bedding and clothing. The boots assigned to the zeks rarely fit (cloth has to be added or taken out, for example), and the thin mittens issued are easily ripped.
The prisoners are assigned numbers for easy identification and in an effort to dehumanize them; Ivan Denisovich's prisoner number is Щ-854. Each day, the squad leader receives their work assignment for that day, and the squad are then fed according to how they perform. Prisoners in each squad are thus forced to work together and pressure each other to get their task done. If any prisoner is slacking, the whole squad will be punished. Despite this, Solzhenitsyn shows that a surprising loyalty exists among the work gang members, with Shukhov teaming up with other prisoners to steal felt and extra bowls of soup; even the squad leader defies the authorities by tar-papering over the windows at their work site. Indeed, only through such solidarity can the prisoners do anything more than survive from day to day.