The story begins with a nameless, first person narrator who is ready to share with you a rather remarkable tale. His story begins in the summer of 1860, with Roger Button, a socially prominent man who owns a hardware company in Baltimore. Roger heads to the hospital to meet his newborn son, only to find that his "baby" is actually a 70-year-old man.
It turns out that Benjamin Button (as the "baby" ends up being called) ages in reverse. He was born at 70 and gets younger at the same rate that everyone else gets older. His parents are filled with shame at their abnormal child and force him to act like a baby, even though Benjamin has the body and mind of a much older man. (He ends up being great friends with his grandfather.) Most people blame Benjamin for his peculiarity – they wish he could just start acting normally – but Benjamin takes the whole thing in stride. He’s a pretty easy-going guy.
When Benjamin appears fifty (and has actually been alive 20 years), he meets and falls in love with the beautiful young Hildegarde Moncrief. Luckily for Benjamin, Hildegarde has a thing for older men, and the two marry and have a son, Roscoe. Unfortunately, as Hildegarde gets older, Benjamin gets younger – he quickly loses interest in his wife.
Benjamin heads off to the Spanish-American War, getting younger every year. By the time he returns, he and his son are pretty close in apparent age, much to his son’s dismay. Benjamin continues to grow younger and finally enrolls at Harvard when he looks about eighteen. By the time he graduates, he’s young enough to go to prep school. Roscoe is increasingly dismayed with his father, especially since Roscoe’s own son is approaching Benjamin’s apparent age. The two of them – Benjamin and his grandson – end up playing together as children.
Eventually, Benjamin is young enough to go kindergarten, and finally too young even for that. As he gets smaller and smaller, he forgets all the things he’s ever done in life. At last, Benjamin can sense only colors and the smell of milk, and finally even those small sensations fade away into darkness.