Best friends Callum and Sephy are at their secret spot on the beach, where they kiss to see what it’s like. Sephy is almost 14 and is thrilled that 15-year-old Callum will be attending her school this year to integrate it. Callum, though, isn’t sure he and Sephy should act like friends at school—he’s a nought and she’s a Cross, and noughts and Crosses don’t mix. That night, Sephy overhears her father, Mr. Hadley, meeting with a nought man and saying that he’s angry “blankers” (a terrible slur for noughts) are attending his daughter’s school.
The first day of school is horrible for Sephy and Callum both. A mob outside protests the nought students, and Sephy gets the mob to disperse by screaming that her classmates are acting like “blankers.” Callum is hurt and offended, so Sephy agrees not to use the slur again.
Over the next few weeks, life gets harder for Sephy and Callum. At home, Callum’s mum and dad fight about how to best fight for racial equality, while his brother Jude and sister Lynette (who’s mentally ill and suffers delusions that she’s a Cross) butt heads. Callum also starts to suspect that Dad and Jude are part of the Liberation Militia, an underground resistance group. Meanwhile, Sephy tries to help the noughts at school by sitting with them at lunch, but the school punishes her for this, and three girls viciously beat her up in retaliation. Sephy’s actions offend Callum and make him feel angry and ashamed, and Callum’s lack of enthusiasm makes Sephy feel bad just for being a Cross. She also becomes uncomfortably aware of how racist her culture is, and she fears that her parents will divorce as their fighting escalates.
Callum gets home one day to find Jude and Lynette exchanging blows. To stop all three children from fighting, Dad tells Jude and Callum why Lynette is ill: three years ago, she and her Cross boyfriend were beaten for being in an interracial relationship. One night, Lynette leaves the dinner table to go on a walk. Hours later, police come to the house and deliver the news that Lynette was hit by a bus and killed. They say it was an accident, but Callum discovers a letter from Lynette under his pillow admitting she committed suicide. He vows to keep this secret. At about the same time, Sephy’s mother attempts to commit suicide but survives.
Sephy is the only Cross to attend Lynette’s funeral, but her presence isn’t well-received; Dad and Jude both tell her to leave. In the weeks after the funeral, Callum realizes that Dad and Jude are becoming more involved with the LM. Mother’s drinking escalates, which frightens Sephy—but her sister Minnie says they shouldn’t do anything.
Six months after Lynette dies, Callum and Sephy decide to meet at the mall—but Jude tells Callum very seriously not to go. Suspecting the worst, Callum races for the mall and drags Sephy out—just before a bomb explodes, killing seven people. Enraged when she realizes that Dad and Jude were involved, Mum slaps Dad so hard she breaks her finger. At the hospital, so she can receive treatment, Mum allows the nurse to scan Callum and Jude’s ID cards, which are linked to their fingerprints. That night, to help herself sleep, Sephy tries wine for the first time.
The next week is tense at the McGregor house, as Mum attempts to kick Dad out. But one night, police come to the house and arrest everyone except Jude, who is out. After a full night of interrogations, Mum and Callum learn that the police have identified Jude as the bomber—but also that the police are charging Dad with the crimes. Mum and Callum hire a nought lawyer, Mr. Stanhope, who insists Dad’s case is a lost cause. But when he visits Dad, Mum and Callum learn that the police told Dad that they had Jude in custody, and that they would release him if Dad confessed to the bombing. Dad is enraged when he learns the police don’t have Jude, but there’s no way to take back his confession.
Sephy watches the case unfold on the news from home, and she knows Dad is innocent. Callum is suspended from school for no reason, but he’s somewhat hopeful about Dad’s prospects when an anonymous benefactor—presumably Sephy—pays for one of the best lawyers in the country, Kelani Adams, to represent Dad. But though Dad pleads not guilty to all the charges, and though Kelani mounts an impressive case, the jury finds Dad guilty of all the charges.
One hot afternoon, Mother makes Sephy put on an expensive dress to go to some undisclosed location. Sephy enters Hewmett Prison extremely confused and doesn’t realize she’s at Dad’s execution until guards bring him out to the scaffold. However, just before Dad is killed, the prison governor stays the execution. When Mum and Callum get to see Dad hours later, Dad says he’s done fighting. Sephy is extremely disturbed by the day’s events—and is then confused when she learns Mother paid the McGregors’ legal fees. She goes to bed and cries herself to sleep.
Sephy wakes in the middle of the night to rocks hitting her window—it’s Callum. He climbs up to her bedroom, enraged by all Crosses’ behavior and half-wanting to take it out on Sephy. Instead, though, he lies down with Sephy, and she falls asleep. Callum considers hurting her but kisses her instead. He sneaks out in the morning. Not long after, Dad dies when he’s electrocuted by the prison fence.
Months later, out of the blue, Jude approaches Callum at a burger joint and invites him to join the LM. Feeling he has no other options, Callum agrees. At the same time, Sephy’s parents have finally agreed that she can go away to boarding school—but Sephy writes Callum a letter asking him to run away with her instead. Callum doesn’t read the letter until it’s too late, so he and Sephy part ways for two and a half years. During this time, Callum works his way up the LM ranks, hurting and killing Crosses and losing his humanity in the process. Sephy quits drinking, finds herself at school, and joins a resistance group. She decides to be a lawyer like Kelani Adams when she grows up.
After finishing school, Sephy unwillingly returns home. She’s shocked to find a letter from Callum, inviting her to meet him on the beach. Sephy goes to the beach—but Callum is there with his LM cell (which temporarily includes Jude) to kidnap Sephy and extract a ransom out of Mr. Hadley. The cell takes Sephy to a remote house, where Jude makes Callum prove his loyalty to the LM by tasking Callum with cutting Sephy’s finger, smearing the blood on a shirt, and filming Sephy reading the demands for her father.
The cell is expecting the General of the LM’s second-in-command to visit them at their remote location, but Callum is immediately suspicious of the man, Andrew Dorn. When Andrew asks to see Sephy, Sephy visibly startles at the sight of him. The next day, Andrew, Jude, and three other members of the cell, Morgan, Leila, and Pete, leave to deliver more demands to Mr. Hadley, leaving Callum to guard Sephy.
Alone in the house together, Sephy and Callum have sex, and Sephy instantly bursts into tears afterwards. Jude and Morgan return before Sephy and Callum are fully dressed and while Sephy is still crying. They conclude that Callum raped Sephy, and they share that someone told the police about them: police arrested Leila, Pete is dead, and Andrew is gone. Jude and Callum fight and while they’re distracted, Sephy runs away into the woods. Callum finds her before Jude or Morgan can, and he points her toward safety. Before she leaves, Sephy shares that Andrew is working with Mr. Hadley—Andrew is the man she saw meeting with Mr. Hadley years ago. Sephy gets home safely, and Callum, Morgan, and Jude split up for their safety.
Five weeks after returning home, Sephy discovers she’s pregnant. Though Minnie initially agrees to keep Sephy’s pregnancy a secret, she ultimately tells Mother and Mr. Hadley. Mr. Hadley insists that Sephy get an abortion, but she refuses. Callum learns about Sephy’s pregnancy on the radio a few months later, and he heads home to see her.
Callum and Sephy meet in the Hadleys’ rose garden, but the police ambush them and arrest Callum. Nobody will believe Sephy or Callum that he didn’t rape her, though Sephy begins speaking publicly about not having been raped. Following Callum’s trial, in which he’s found guilty, Mr. Hadley makes a final attempt to manipulate the couple: he tells them both that if Sephy gets an abortion, he won’t let the authorities hang Callum. They reject his manipulation, and Callum screams that he loves Sephy as he’s hanged. Not long after, Sephy gives birth to a baby girl.
