Ellen Thatcher is born to Ed Thatcher, an accountant, and his wife Susie. Meanwhile, Bud Korpenning arrives in New York by boat, ready to get a job and make a living. George Baldwin, a frustrated young lawyer, hears of a milkman being hit by a train car and takes on the case. The milkman is Gus McNeil; his wife Nellie begins an affair with the smitten Baldwin.
Jimmy Herf, a young boy, arrives in the city with his mother Lily, who suffers a stroke and dies soon thereafter. Jimmy is left in the care of his aunt and uncle, who would like to see him go to Princeton or Yale and attain financial success. Jimmy, however, has other plans, and goes into journalism.
By this point, Bud has thrown himself off the Brooklyn Bridge in desperation and Ellen has become an actress on the New York stage. She is quite the sensation, and the suitors begin to pile up. Meanwhile, Joe Harland, an older cousin of Jimmy's and a man who was once highly successful in the stock market, has become an impoverished drunkard. Stan Emery, a new character, is likewise a hard drinker -- a Harvard student thrown out of his school and prone to raising Cain about town. He and Ellen, who is married to John Oglethorpe, begin a heated affair, while Jimmy, a friend of Stan's, looks on.
Baldwin has also fallen for Ellen. Gus McNeil, now a wealthy man and a rising politico, tries to persuade him to run for office, but Baldwin shies away from the idea. He seems more focused on other matters -- his practice, the difficult situation with his estranged wife Cecily, and his deepening love for Ellen. Finally he collapses in a fit of jealousy and pulls a gun on the ever-flirtatious Ellen in a roadhouse.
By now World War I has broken out, and Jimmy expresses his desire to go to Europe. Meanwhile, Stan impulsively marries a girl named Pearline, thereby breaking Ellen's heart. Not long after, the young man dies in a fire. We learn that Ellen is pregnant with his baby and is determined to have it and raise it.
When we next meet the characters, World War I is over and the soldiers -- among them Jimmy's cousin James Merivale -- are returning home. Jimmy and Ellen have married while in Europe together, and they sail to New York with the baby Martin -- Stan's son, we presume. Meanwhile, Baldwin has decided to run for office on a reform ticket, a decision which angers the reactionary Gus McNeil.
It is the era of Prohibition, and Congo Jake, a French sailor and a friend of Jimmy's, has made a massive amount of money through bottlegging. Near the novel's end, we meet Congo again -- now named Armand Duval and a Park Avenue millionaire. His rise to wealth is mirrored by the downward spiral of Dutch Robertson, a returning veteran who is driven to crime by poverty and is sentenced to twenty years in prison.
All is not well for Ellen and Jimmy, whose marriage seems to be quickly crumbling. Jimmy demands Ellen, who has quit the stage, if she still loves him; she tells him "no." Jimmy throws away his job as a journalist and professes to friends his plans to leave the city. He and Ellen divorce, she marries George Baldwin, and the last we see of Jimmy is the beginning of his long trip away from New York.