Duplicity
One of the key themes of the novel is duplicity and the way in which people take advantage of the suffering of others in order to gain something for themselves. The most duplicitous character in the novel is Kate, who seems to thrive on keeping secrets and devising plots. When she meets Milly and realizes that Millie is deathly ill, she also realizes that it will not be long until her death, and that Milly will leave behind a substantial fortune. Kate plans that Merton will court Milly and marry her after a whirlwind romance, shortly inheriting Milly's vast wealth after her imminent death. Kate also remembers to be careful about the information she shares with Milly, keeping her engagement to Merton a secret.
The Unbeatable Nature of Tuberculosis
At the start of the twentieth century, tuberculosis was one of the most deadly diseases, and it did not respect socio-economic boundaries, unlike many diseases of the day. Even a woman with Milly's means was powerless to beat the disease, despite having access to the best physicians in the world.
Love
One of the novel's main themes is love, and it is shown to be a very complex concept. We learn at the start of the story that Kate and Merton are betrothed and that they are anxious to get married, which indicates that they are very much in love. However, Merton develops a strong relationship with Milly while both are in America, and Milly falls in love with him, although she never admits this to anyone. Merton believes that he loves Kate, but he also has genuine feelings for Milly, which is why he feels tremendously guilty after her death, which he feels was hastened by his betrayal of her love. Kate believes she has done everything because of her love for Merton, but she has also encouraged him to marry another woman, so it is likely that she is more attracted to money than she is to Merton.
Human Motivation
James uses the novel to show the many different ways in which people react to the troubles of others. Although everyone rallies round Milly and seems to be doing everything in her best interests, their motivations for doing so are completely different. For example, Kate provides much needed friendship to Milly, but it is not a genuine friendship, because Kate sees Milly's illness as an opportunity to set herself up financially with or without Merton by her side. Merton goes along with the plan for a while, but it is clear that he is conflicted internally about it.
Remorse
At the end of the novel, it appears that Merton is feeling a sense of remorse. He believes that Milly's death was hastened by his betrayal of her. She had loved him genuinely, and finding out that his love for her was less than genuine sends her health into a decline. She seems to give up the will to live, and Merton feels responsible for this. Because of this remorse, he refuses to accept the money she leaves him, and also demands the same from Kate as a condition of marriage.
