Seventeen-year-old America Singer lives in the futuristic kingdom of Illéa, where the society is divided into eight castes. Caste One is made up of royalty. Eight encompasses the poorest people. America and her family are Fives.
Earlier in “The Selection” trilogy, America received an invitation to register for a televised competition called the Selection.The winner would get to marry Maxon Schreave, the prince of Illéa. She struggled to choose between the prince and her poor, secret boyfriend, Aspen.
With her mind finally set on Maxon, America knows she has to win the prince from her competitor, Kriss. America treads cautiously around Maxon’s father, King Clarkson, who believes she is not obedient or ladylike enough to be the next queen.
The palace has been under attack from two separate rebel groups. The king leaves the country unexpectedly. In his absence, northern rebel leaders August Illéa and his fiancée, Georgia Whitaker, come to the palace at night and request an audience with Maxon and America. August is a direct descendant of the country’s founder, Gregory Illéa, but is not interested in taking the crown. Instead, he supports Maxon but wants nominated officials and an end to the caste system.
He tells Maxon that the southern rebels want to take over Illéa and end the monarchy but have no intenion of keeping their promises to the nation’s poor. August wants Maxon to choose America as his wife, as they admire her bravery and believe she would support their plan. Maxon is outraged at being told whom to marry, and America is upset that she is being used as a pawn in their revolution.
A few days later, during the live taping of The Report (the weekly state of the country address), King Clarkson announces that rebels have been attacking people by the castes of the women in protest of the Selection. All the participants are fearful, but when it’s America’s turn to speak to the people of Illéa, she tells them to fight the rebels back with whatever they have. Once again, the king is upset with America.
Maxon surprises America with a date to the roof of the palace. They get caught in the rain, dance and kiss. America realizes that she is in love with Maxon, but she doesn’t tell him.
Maxon suspects that the rebel attacks are getting worse, but his father won’t tell him the truth. America comes up with a plan to sneak out of the palace and meet with August and Georgia to find out what’s going on in the rest of country. She and Maxon both dress as Sixes and sneak out of the palace in a food supply truck.
Aspen and other officers take them to the meeting spot in town where August reveals that several hundred people have already been killed by southern rebels. He asks Maxon for weapons so that the northern rebels can fight the southerners, but Maxon has to consider how wise it is to arm rebels. When America and Maxon leave, they are attacked by a group of southern rebels with guns. They manage to escape and return to the palace.
The palace holds a tea party where each of the Elite has to invite two guests. America invites the Italian princess Nicoletta and Georgia under the guise that the girl is a friend from home. When they all meet, Georgia explains the goals of the northern rebels to Nicoletta and asks her to provide weapons so they can fight the southern rebels. Nicoletta agrees to the request, as Italy wants to be Illéa’s ally, but does not support the current caste system and other human rights violations.
The Elite prepare for the Convicting, an event where the girls must publicly convict a criminal to serve prison time. Maxon gives America a set of earrings and a matching bracelet, as is tradition. The other Elites condemn the criminals they are presented with to jail, but America can’t bring herself to punish a thief who stole clothes for his children. She gives him the jewlery so he can save himself from prison. The enraged king demands that Maxon kick America out of the Selection. Maxon insists that she is now too popular to leave; he eventually convinces the king to allow her to stay.
A few days later, just as America prepares to tell Maxon her true feelings of love, a guard arrives with news that her father, Shalom, has died from a heart attack. She returns to her home in Carolina for the funeral. America's mother gives each of her three eldest children a letter from their father, written before his death. In America's letter, Shalom tells her he loves her and is proud of the woman she has become. He also tells her to "look unto the North Star." America pieces together hints and memories and realizes that her father was a northern rebel.
America’s brother, Kota, is upset that Shalom left him only the family home, which leads to an argument with America. Spitefully, Kota reveals that he knows about America’s relationship with Aspen and asks her if Maxon knows. America decides that it’s time for her to tell Maxon the entire truth before he finds out from someone else.
After a party back at the palace, Maxon tells America he has chosen her to be his wife and the future queen. They begin to kiss passionately and undress until they are startled by a noise in the hallway outside America’s room. Maxon tells America that he wants to wait and take her on a proper honeymoon where it’s private. She agrees, asks him to stay and sleep beside her.
The next morning while still in bed, Maxon tickles America. She screams in laughter. Aspen, the guard outside her room, rushes in thinking America is in danger and finds her and Maxon in that intimate moment. America goes to talk to Aspen, and Maxon realizes that Aspen was America’s first love. Hurt by America’s betrayal, Maxon tells her that he can't marry her and orders Aspen to leave. America tries to explain the situation, but Maxon refuses to listen and leaves with Kriss.
America must still attend the engagement ceremony and prepares herself to hear Maxon announce Kriss as his choice. All the Selected girls are there, along with August, Georgia and other northern rebels in disguise. Suddenly, southern rebels dressed as guards start shooting, killing several people, including some of the Selected. A southern rebel shoots at America, but Maxon leaps in front of her and gets shot instead. Bleeding profusely, he apologizes to America for almost not choosing her, saying that he loves her to his last breath and that his heart belongs to her.
Aspen rushes over to save them both, but Maxon orders him to save America instead. Aspen obeys, taking her to a safe room and locking her in. America tries to escape from the safe room by using a gun to shoot at the locks, but is unsuccessful. When she is finally rescued from the room by northern rebels, she is told that the fight is over. The palace guards and the northerners managed to fight back the southerners with the weapons Nicoletta provided.
America is taken to the hospital for shock. While there, she sees Aspen severely injured but alive. America is terrified that Maxon is dead, as she can’t find him in the hospital. Aspen tells her that Maxon is alive and is now the king, as both King Clarkson and Queen Amberly were killed in the attack. Aspen also tells America that while he still cares about her, he isn't in love with her anymore. Lucy, one of America’s maids, runs to Aspen and kisses him, revealing that they are in a relationship. America is happy for them and leaves to find Maxon.
She goes to Maxon’s room where he is recovering from the gunshot. He tells her his plans to dissolve the castes, starting with the Eights merging with the Sevens. He then proposes to her; America accepts.
In the book’s epilogue, it is America and Maxon’s wedding and coronation day, when they will be joined as man and wife and crowned as the new King and Queen of Illéa. Aspen, who will soon marry Lucy, walks America down the aisle and gives her away to Maxon. As happy as America is, she knows that there are hard times ahead.