The novel's first chapter begins with "All this happened, more or less"; this introduction implies an unreliable narrator tells the story. Vonnegut utilizes a non-linear, non-chronological description of events to reflect Billy Pilgrim's psychological state. Events become clear through flashbacks and descriptions of time travel experiences.[4] In the first chapter, the narrator describes his writing of the book, his experiences as a University of Chicago anthropology student and a Chicago City News Bureau correspondent, his research on the Children's Crusade and the history of Dresden, and his visit to Cold War-era Europe with his wartime friend Bernard V. O'Hare. In the second chapter, Vonnegut introduces Billy Pilgrim, an American man from the fictional town of Ilium, New York. Billy believes that an extraterrestrial species from the planet Tralfamadore held him captive in an alien zoo and that he has experienced time travel.
As a chaplain's assistant in the United States Army during World War II, Billy is an ill-trained, disoriented and fatalistic American soldier who discovers that he does not like war and refuses to fight.[5] He is transferred from a base in South Carolina to the front line in Luxembourg during the Battle of the Bulge. He narrowly escapes death as the result of a string of events. He also meets Roland Weary, a patriot, warmonger, and sadistic bully who derides Billy's cowardice. The two of them are captured in 1944 by the Germans, who confiscate all of Weary's belongings and force him to wear wooden clogs that cut painfully into his feet; the resulting wounds become gangrenous, which eventually kills him. While Weary is dying in a rail car full of prisoners, he convinces a fellow soldier, Paul Lazzaro, that Billy is to blame for his death. Lazzaro vows to avenge Weary's death by killing Billy, because revenge is "the sweetest thing in life."
At this exact time, Billy becomes "unstuck in time"; Billy travels through time to moments from his past and future. The novel describes the transportation of Billy and the other prisoners into Germany. The German soldiers held their prisoners in the German city of Dresden; the prisoners had to work in "contract labor" (forced labor); these events occurred in 1945. The Germans detained Billy and his fellow prisoners in an empty slaughterhouse called Schlachthof-fünf ("slaughterhouse five"). During the Allied bombing of Dresden, German guards hid their captives in the partially underground setting of the slaughterhouse; this protected those captives from complete annihilation. As a result, they are among the few survivors of the firestorm that raged in the city between February 13 and 15, 1945. After V-E Day in May 1945, Billy was transferred to the United States and received an honorable discharge in July 1945.
Billy is hospitalized with symptoms similar to post-traumatic stress disorder and placed under psychiatric care at a Veterans Affairs hospital in Lake Placid. During Billy's stay at the hospital, Eliot Rosewater introduces him to the work of an obscure science fiction writer named Kilgore Trout. After his release, Billy marries Valencia Merble, whose father owns the Ilium School of Optometry that Billy later attends. Billy becomes a successful and wealthy optometrist. In 1947, Billy and Valencia conceive their first child, Robert, on their honeymoon in Cape Ann, Massachusetts. Two years later, their second child, Barbara, was born. On Barbara's wedding night, Billy is abducted by a flying saucer and taken to a planet many light-years away from Earth called Tralfamadore. The Tralfamadorians have the power to see in four dimensions; they simultaneously observe all points in the space-time continuum. They universally adopt a fatalistic worldview: death means nothing to them, and their typical response to hearing about death is "so it goes."
The Tralfamadorians transport Billy to Tralfamadore and place him inside a transparent geodesic dome exhibit in a zoo; the inside resembles a house on planet Earth. The Tralfamadorians later abduct a pornographic film star named Montana Wildhack, who had disappeared on Earth and supposedly drowned in San Pedro Bay. The Tralfamadorians intend to have her mate with Billy. Montana and Billy fall in love and have a child together. Billy is instantaneously sent back to Earth in a time warp to re-live past or future moments of his life.
In 1968, Billy and a co-pilot are the only survivors of a plane crash in Vermont. While driving to visit Billy in the hospital, Valencia crashes her car and dies of carbon monoxide poisoning. Billy shares a hospital room with Bertram Rumfoord, a Harvard University history professor researching an official war history. They discuss the bombing of Dresden, which the professor initially refuses to believe Billy witnessed. Despite the significant loss of civilian life and the destruction of Dresden, the professor regards the bombing as a justifiable act.
Billy's daughter takes him home to Ilium. He escapes and flees to New York City. In Times Square he visits a pornographic book store, where he discovers books written by Kilgore Trout and reads them. He discovers a science fiction novel titled The Big Board at the bookstore. The novel is about a couple abducted by extraterrestrials. The aliens trick the abductees into thinking they are managing investments on Earth, which excites the humans and, in turn, sparks interest in the observers. He also finds some magazine covers that mention Montana Wildhack's disappearance. While Billy surveys the bookstore, one of Montana's pornographic films plays in the background. Later in the evening, when he discusses his time travels to Tralfamadore on a radio talk show, he is ejected from the studio. He returns to his hotel room, falls asleep, and time-travels back to 1945 in Dresden. Billy and his fellow prisoners are tasked with locating and burying the dead. After a Maori New Zealand soldier working with Billy dies of dry heaves the Germans begin cremating the bodies en masse with flamethrowers. German soldiers execute Billy's friend Edgar Derby for stealing a teapot. Eventually all of the German soldiers leave to fight on the Eastern Front, leaving Billy and the other prisoners alone with tweeting birds as the war ends.
Through non-chronological storytelling, other parts of Billy's life are told throughout the book. After Billy is evicted from the radio studio, Barbara treats Billy as a child and often monitors him. Robert becomes starkly anti-communist, enlists as a Green Beret and fights in the Vietnam War. Billy is eventually killed in 1976, at which point the United States has been partitioned into twenty separate countries and attacked by China with thermonuclear weapons. He gives a speech in a baseball stadium in Chicago in which he predicts his own death and proclaims that "if you think death is a terrible thing, then you have not understood a word I've said." Billy soon after is shot with a laser gun by an assassin commissioned by the elderly Lazzaro.
