Persephone "Sephy" Hadley is a Cross and the daughter of a wealthy senior politician, Kamal Hadley, who later becomes Prime Minister. Callum McGregor is a Nought, and they used to play together when Jasmine Adeyebe-Hadley, Sephy's mother, employed Meggie McGregor, Callum's mother, as a nanny. Ever since Jasmine fired Meggie, however, Sephy and Callum's friendship has been secret, as such interracial friendships are frowned upon by society.
The two meet again in Heathcroft, a high school for Crosses that now accepts the best-performing Noughts. Sephy is overjoyed to see Callum in her class, but most of her classmates do not accept her association with a Nought. Despite this, she deepens her relationship with Callum, and even sits at a table with Noughts, upsetting Callum, though they eventually make up.
Meanwhile, Callum's elder brother, Jude, and his father, Ryan, join the Liberation Militia (LM), a violent paramilitary organisation against Cross supremacy. Jude and Ryan are accused of participating in the LM bombing of Dundale Shopping Centre, and Callum is also accused after he told Sephy to leave the shopping centre. He is ultimately spared due to a lack of evidence. Callum has to leave school, and Ryan faces the gallows. Jasmine, remembering her prior friendship with the McGregor family, secretly hires a prominent Cross lawyer to defend Ryan. Escaping hanging, Ryan is given a life sentence but is killed by an electric fence, supposedly in an escape attempt.
Sephy decides to start anew and persuades a reluctant Jasmine to let her attend a boarding school, Chivers. She hasn't heard from Callum in a week, so she writes a letter asking him to run away with her and that if he doesn't contact her, she'll be leaving for Chivers. Callum, however, has decided to join the LM, and doesn't read the letter until it's too late. He sprints to her house and fails to catch up to the car as it pulls out of the driveway. Having not seen Callum running behind, Sephy concludes that their friendship is no longer as important to him as she had thought.
Years later, Sephy returns home from Chivers. Upon entering the house, she discovers a letter by Callum telling her to meet him at the family's private beach. She goes there, but discovers Callum is there with other LM members to kidnap her and hold her hostage. She's taken to their hideout and the LM members demand the release of at least five LMs and a ransom for Sephy. The LM's second-in-command, Andrew Dorn, then visits Callum and his cell members.
Callum is able to visit an injured Sephy in the room where she is being held. Alone together, Callum reveals to her his unsuccessful attempt to catch up to her before she left for Chivers. Their love rekindles, and the two end up having sex. Afterwards, Sephy escapes into the woods, chased by Jude and another LM member. Callum finds her first and gives false directions to the others; he then gives Sephy instructions to escape. Sephy then tells Callum that she'd seen Andrew before in her house with Kamal, revealing that Andrew is a government informant. Informing the rest of the LM about Andrew, the remaining members agreed to split up and keep a low profile, not meeting up again until Callum's birthday.
Sephy then begins to experience strange symptoms, and takes a pregnancy test, revealing that she is pregnant with Callum's child. When her parents learn of this, they pressure her to have an abortion, which Sephy repeatedly refuses. Meanwhile, Callum is working as a mechanic as a cover, and hears Kamal on the radio being interrogated over whether his daughter is pregnant. Callum then meets up with Sephy in the Hadleys' rose garden, and she confirms the rumors. While they're meeting, they are discovered and Callum is arrested. Nobody believed Sephy when she maintains she was not raped, and Callum is sentenced to be hanged.
Kamal tells Sephy that if she keeps her child, Callum will be hanged, but if she has the abortion, he will serve years in prison instead. Kamal makes a similar offer to Callum, wanting Callum to publicly admit to raping Sephy. Both decide to keep the baby, and Callum is hanged at the gallows.
