Claire Messud's The Emperor's Children follows three friends living up to New York City in the days preceding 9/11. Danielle, Marina, and Julius are each struggling to establish themselves at 30-years-old. Their lives interweaves in complicated ways: asking favors, drama, advice, etc. While they each try to improve their circumstances, none of them seems to get their lives together by the end of the book.
By making the three main characters the exact same age, Messud is drawing a parallel between their lives. She wants to use them to illustrate different approaches to middle age. For example, Danielle is the most put-together of the three. She approached adulthood with a systematic approach, focusing on career first, then diverging. She's compromised a lot of fun in order to hone in on her career, but at least she is established in that sphere. For her part, Marina has thrown herself into a passion project -- a book -- which is now late to finish and desperate. She's not a successful author. After meeting Seeley, her new editor, however, she quickly re-strategizes. They get married before the end of the book. Finally, Julius has partially developed a career, but he can't support himself on just his journalism work, so he works some part time jobs. He hates it. Lonely and approaching a breaking point, he pursues the somewhat younger and more successful, David Cohen. Eventually he moves in with Cohen and becomes his stay-at-home significant other. That relationship is unsuccessful, and falls to shambles when Cohen loses his job.
Each of these characters finds a foil in Bootie, Marina's cousin. He's dropped out of college and moved in with his aunt and uncle for a while, trying to become self-employed. For all the complacency, resent, and laziness of his counterparts, Bootie is ambitious and industrious. His attitude earns him a job from his uncle, but he quickly uncovers corruption in Thwaite's company. Refusing to compromise his values, he published an expose on Thwaite's illegal and unethical practices. Bootie's interactions with Danielle, Marina, and Julius prove challenging because he represents everything they had hoped to be but have not abandoned hope at becoming. He inspires them to change, however. For example Marina faces the truth of her entitlement and decides to focus on improving herself for Seeley's benefit. This is why Bootie supposedly dies in the attack on 9/11; he's a savior character. An additional messianic parallel is in his discovery in Florida by Danielle sometime later. Unlike the other's whose dreams have died, young Bootie makes an entirely new life for himself. He's eager and creative, committed to change. This is why even tragedy can't stop his success.