In England Ka'iulani struggles to fit in, as her Polynesian heritage makes her a target of racism and offensive stereotypes from the Europeans she meets. She does make some friends, including the handsome young Clive Davies. They develop a relationship and the two become engaged. But one day her father returns from Hawai'i after several years, and to her shock he informs her that her uncle, King Kalakaua, died shortly after being forced to sign the new constitution by Thurston and Sanford B. Dole. He then informs her that after a failed native rebellion against the new constitution Thurston had enough support to arrest and depose Queen Liliuokalani, overthrowing the monarchy. After discovering that the Davies family knew of her family's overthrow but hid the news from her Ka'iulani decides to call off her engagement and leave England. She travels to the United States, where she gathers media attention and denounces the overthrow as well as the U.S.'s involvement. Her cultured, regal appearance overcomes the racist views against her and many note that she is not the "Barbarian Princess" she was depicted as, at all. Her campaign against the overthrow climaxes with her meeting U.S. President Grover Cleveland. At a lunch with the President, Ka'iulani charms him and convinces him to actively oppose the overthrow, which he does so by refusal to annex Hawaii as an American territory. Unfortunately for Ka'ilulani, this was done during the waning days of the Cleveland administration, as a few weeks later President William McKinley is inaugurated.
Unfortunately, when Ka'iulani returns to Hawai'i she learns the U.S. has not only failed to oppose the overthrow but has also accepted Thurston's annexation proposal, annexing Hawai'i as a territory of the United States of America. She attends a small private funeral for the Kingdom of Hawai'i hosted by her aunt, Queen Liliuokalani. Shortly after her return she is visited by Sanford B. Dole, who explains that three U.S. legal commissioners are arriving and that he and Thurston would like the Princess to host a small dinner for them. Though she's appalled at the impertinent request, he convinces her that it might be to her advantage too. At the dinner Ka'iulani charms her visitors before surprising Thurston by publicly petitioning for an amendment to the annexation treaty guaranteeing universal suffrage and voting rights to all Native Hawaiians. She is disregarded by an appalled Thurston, who points out she is not a recognized diplomat, before Dole stands up for the princess and declares he will petition the amendment for her. As the amendment gathers support amongst the dinner guests, Thurston leaves, embarrassed and angry.
After the dinner Ka'iulani is surprised to learn that Clive has come to Hawai'i, as he had promised he would, and she goes to see him. He tells her that his father passed and he is now in charge of his assets, including those in Hawai'i. The two make up and Clive asks Ka'iulani to return to England and marry him. She refuses, stating that her future is in Hawai'i. When he equally refuses to move to Hawai'i, the two share a last farewell kiss before Clive leaves for England. The film ends with Ka'iulani returning her treasured seashells, which she had kept throughout her travels to remind her of Hawai'i, back to the ocean as she wades in the waves, with a voiceover saying that the bright flame of Ka'iulani is kept alive by the love of her people. A post-credits card shows that Ka'iulani died less than one year after annexation, some say of a broken heart for the loss of her kingdom. Another card mentions that in 1993 President Clinton signed the Apology Resolution, apologizing to Hawai'i for the role the U.S. played in the overthrow.
