The narrative follows the life of Oskar Matzerath, as he recounts his experiences while confined in a mental hospital from 1952 to 1954. Born in 1924 in the Free City of Danzig (modern-day Gdańsk, Poland), he possesses the understanding and insights of an adult but resolves never to mature upon hearing his father’s proclamation that he would become a grocer. Endowed with a remarkable shriek, capable of breaking glass or serving as a form of defense, Oskar identifies as one of those "clairaudient infants" who believes his "spiritual development is complete at birth and only needs to affirm itself". He maintains his childlike stature while navigating the challenges of World War II, engaging in several romantic entanglements, and experiencing the tumultuous landscape of postwar Europe. A cherished gift from his third birthday—a toy tin drum—remains his constant companion, with multiple replacements acquired whenever he exhausts one through enthusiastic play, illustrating his unwavering determination to protect it, even resorting to violence if necessary.
Oskar perceives himself as having two "presumptive fathers": Alfred Matzerath, his mother's husband and a member of the Nazi Party, and Jan Bronski, her cousin and lover, who is executed for his defense of the Polish Post Office during Germany’s invasion. Following the death of his mother, Alfred weds Maria, a woman who inadvertently becomes Oskar’s first lover. After their marriage, Maria gives birth to Kurt, whom Oskar claims as his son. However, Oskar is disheartened that Kurt continues to grow, refusing to join him in his decision to remain eternally a child at age three.
Amidst the war, Oskar becomes part of a troupe of performers—dwarfs who entertain German soldiers at the front lines. Tragedy strikes when his second love, the small-statured Roswitha, is killed by Allied forces during the Normandy invasion, prompting Oskar to return to his family in Danzig, where he ultimately leads a gang of young criminals reminiscent of the Edelweiss Pirates. When the Red Army seizes Danzig, Alfred faces a grim fate; he succumbs to a seizure and is shot by invading soldiers after attempting to swallow his party pin to conceal his identity as a Nazi. The weight of guilt hangs over Oskar, as he feels partially responsible for the deaths of his two father figures—leading Jan to the Polish Post Office for drum repairs and returning Alfred's Nazi pin during a Soviet interrogation.
Post-war, Oskar, along with his widowed stepmother and their son, must leave Danzig, now part of Poland, and relocate to Düsseldorf. There, he takes on modeling for nude photographs and engraving tombstones. Rising tensions prompt Oskar to separate from Maria and Kurt, moving into a flat owned by the Zeidlers. In this new abode, he falls for Sister Dorothea, a neighbouring woman, but ultimately fails to win her affection. During a chance meeting with fellow musician Klepp, Oskar is challenged about his authority over musical judgment and, eager to prove himself, he picks up his drum and begins to play, breaking his vow to refrain from drumming since Alfred's demise. This impulsive act leads to the formation of the Rhine River Three jazz band, alongside Klepp and Scholle, a guitarist. Their talent soon catches the eye of Mr. Schmuh, who offers them a gig at the Onion Cellar club. Following a stellar performance, Oskar, now a recognized jazz drummer, is approached by a talent scout who presents him with a lucrative recording contract.
Fame and wealth come to Oskar, but so does tragedy. One day, while strolling through a field, he discovers a severed finger—the ring finger of Sister Dorothea—who has met a grisly end. In a twist of fate, he meets and develops a friendship with Vittlar. In an act of self-sacrifice, Oskar allows himself to be wrongfully convicted of Dorothea's murder and is subsequently confined to an asylum, where he begins to pen his memoirs, chronicling a life filled with extraordinary events and deep emotional tumult.
