The story revolves around the life of Oskar Matzerath, as narrated by himself when confined in a mental hospital during the years 1952–1954. Born in 1924 in the Free City of Danzig (now Gdańsk, Poland), with an adult's capacity for thought and perception, he decides never to grow up when he hears his father declare that he would become a grocer.
Gifted with a piercing shriek that can shatter glass or be used as a weapon, Oskar declares himself to be one of those "clairaudient infants", whose "spiritual development is complete at birth and only needs to affirm itself". He retains the stature of a child while living through the beginning of World War II, several love affairs, and the world of postwar Europe.
Through all this, a toy tin drum, the first of which he received as a present on his third birthday, followed by many replacement drums each time he wears one out from over-vigorous drumming, remains his treasured possession; he is willing to commit violence to retain it.