14-year-old Marcus Frederick resides in Manhattan's Lower East Side with his grandmother, Lucy. His mother Joanne has spent the last nine years in prison for smuggling undocumented people into New Mexico, while his father is presumed dead in a car accident when Marcus was five. Lucy runs her own bar, Lucy's, which gives Marcus a lot of unsupervised time to roam with his four friends—Benny, Louis, Harold, and Chip—sharing idle hours in their underground clubhouse near the waterfront. Chip longs for bigger heists, while Marcus dreams of moving back to New Mexico to live on a ranch with his uncle Billy, who has promised to mail him an airplane ticket.
One day, while selling stolen merchandise to elementary school kids, Marcus meets 14-year-old Melena. Melena declines his invitation to attend his fifteenth birthday party because her father, Paco, an abusive tow-truck driver, disapproves of her staying out late. That night, Melena sneaks out of her apartment and meets Marcus in front of Lucy's, where she gives him her ski mask as a gift before leaving.
The next morning, Marcus receives a flight ticket to New Mexico in the mail and relays this information to Lucy. Unbeknownst to him, the ticket was sent by Mack, a regular patron at the bar who believes it would do Marcus good to leave the city.
Marcus, Benny, and Louis are then introduced to Justin and Shane, Chip's Miami-based drug-dealing friends. Marcus confides in Melena about his plan to travel to New Mexico and asks her to join him, but she turns him down because she knows her father would never approve and she cannot afford the ticket.
When Marcus is hauled to the police station for continuing to sell stolen goods, a detective named Hank reveals that his mother is in prison for murder, not the smuggling she had claimed. Marcus visits Joanne and explains his plan to Melena; Joanne explains that her husband was abusive toward her and Marcus, and she hadn’t known how to tell him without upsetting him. She also reveals her parole hearing isn’t until four years later, but promises they will go to New Mexico once she is out.
Marcus' friends plan a burglary of a policeman's apartment for valuables, but Marcus refuses to participate. Paco drives to the clubhouse where Melena and Marcus often gather. He confronts them and harshly disciplines Melena before leaving with her. A vengeful Marcus rides his bicycle to Melena's apartment and knocks Paco out cold.
Marcus and Melena run away and camp in a tent for the day, planning to meet at Penn Station at noon the next day to board the train. To fund the train fare, Marcus agrees to join his friends in the robbery, while also grappling with the fear of exposing himself to the police. In his search for Melena, Paco returns to the clubhouse, where he finds the pair and attempts to reclaim Melena. He is discovered, and, in a tense moment, Harold—after jokingly firing a stolen gun during a darts game to show off—accidentally shoots Paco, who collapses and dies. Marcus uses Paco's tow truck crane to lift Paco's body into a shallow grave, a grisly act that haunts him and heightens his fear of police involvement.
As the day they plan to leave approaches, Marcus discovers that his hidden stash of money has vanished along with the loot from the earlier robbery. Chip is revealed to have a newer, more glamorous acquisition, a brand-new Diamondback bicycle, which Marcus confronts as a sign that something is very wrong. Justin and Shane reveal they were the ones who stole the loot, and the trio brutally beat Marcus before fleeing. Marcus returns to the clubhouse, grabs the gun, and hears an unmarked car and a police cruiser outside. Benny has already reported Paco's murder, and Chip is arrested.
With time running out, Marcus robs a convenience store cashier, Duane, to extract cash for the journey. He races to Penn Station, reunites with Melena, and the two board the train west toward New Mexico. Melena, unaware that her father is dead, fears what will happen when he learns she has left; Marcus, aware of the truth about Paco, remains silent, choosing to protect her from a painful revelation as they step into an uncertain future together.
