The story begins by introducing us to the novel's six (yup, you read that right) narrators, Bernard, Neville, Louis, Jinny, Susan, and Rhoda, who meet as children in a nursery. During this phase of the novel, we learn a lot about the characters' personalities and their relationships to each other.
After looking on as our new friends get embroiled in some kid-level dramas (e.g., trouble in math class and unrequited crushes), the six children head off to their respective boarding schools. At that time, the boys meet Percival, whom everyone seems to revere (and Neville falls in love with). The protagonists then all graduate and proceed into their adult careers (with a stop at university along the way, for some). At some point in there, Percival becomes friends with the girls as well, though we're not sure when that actually occurs.
The narrators' paths diverge quite a bit as the novel progresses. After enduring a stint in a Swiss school, Susan returns to her beloved hometown, gets married, and starts having babies. Meanwhile, Bernard apparently moves to Waterloo (that's not entirely clear, but Woolf drops some clues to that effect), and we're not entirely sure what he does there, other than shave and make up stories about pedestrians. Meanwhile, Rhoda, Louis, Neville, and Jinny go to live in London, and their life paths are all over the map: Louis works for a shipping company, Jinny is a socialite, and Neville is a classics professor (we don't learn Rhoda's profession).
Midway through the book, the friends meet up for dinner in London to see Percival off before he leaves to work in India, at which point Bernard announces that he is getting married. An unspecified amount of time later, Percival falls from his horse in India and dies, and our narrators are devastated. The death occurs just as Bernard's son is born, creating some serious cognitive dissonance for poor Bernard.
The characters then struggle with aging and reflect upon the progress of their lives and adulthood. Toward the end, they all meet up at Hampton Court and experience the aches and pains that come when old friends reconnect after a long time has passed.
The novel ends with Bernard talking to an apparent stranger, attempting to sum up the lives of the six narrators (i.e., the events of the novel) and work out his philosophies of language and life…and that's why the last chapter is fifty pages long. He reflects upon his lifelong struggle to turn his phrasemaking into something meaningful and, despite the major ups and downs he's experienced along the way, he resolves to keep on trying.