The narrative flashes back six years. In St. Louis, Missouri, Veronica has just given birth at home to a son she names Dominic. Her friend Lola assisted with the delivery because Veronica and her partner, Clay Barkley, lack money and insurance. Fearing that a hospital would deem them unfit parents and take their baby, Veronica avoided doctors throughout her pregnancy.

Veronica reflects on her past; she ran away from an abusive home at 16 and subsequently became addicted to drugs. She met Clay, who came from a wealthy family but became addicted to opioids after a skiing accident, leading to his estrangement from his parents. The pregnancy was unplanned but has motivated Veronica to become sober for good.

After Lola agrees to be Dominic’s godmother, Clay arrives with baby supplies. Veronica makes him promise to quit drugs, warning that she will leave with their son if he fails. He agrees and tearfully proposes. Veronica accepts, determined to protect Dominic no matter what.

Two weeks later, Veronica is exhausted from caring for the newborn Dominic, who screams constantly unless he’s nursing or asleep. Sensing that she’s reaching a crisis point, Clay offers to take the baby for a drive to calm him down and buy more diapers. A grateful Veronica hands Dominic to him and immediately falls into a deep sleep.

Veronica wakes up hours later to find the sun setting. She discovers Clay asleep on the sofa but can’t find Dominic anywhere in the apartment. She shakes Clay awake and sees from his dazed expression and pinpoint pupils that he’s on drugs. He’s disoriented and, when pressed, suggests that he might have left Dominic in the car. Veronica races outside to their car, but the back seat is empty; both Dominic and his car seat are gone. She confronts Clay, who can only apologize. Horrified, Veronica decides to call the police.

A police officer named Grenell responds to the call but is dismissive of Veronica’s story. He questions why she has no birth certificate for Dominic and suggests that she might have stolen the baby. Grenell notices Clay’s track marks and interrogates him. Clay admits that he pulled over at a rest stop to take a “nap,” implying that he used drugs and passed out, leaving the exact time of Dominic’s disappearance unknown. Grenell pats Clay down, finds heroin, and arrests him for drug possession. As he leads Clay away, he ignores Veronica’s pleas for help, telling her to get “cleaned up.” Veronica resolves to find her son herself.

Nearly five years later, Veronica still searches for Dominic. After his disappearance, the police suspected that Clay had killed him, but no body was ever found. Veronica eventually moved from St. Louis to New York for a job, donating all of Dominic’s baby items except for a stuffed elephant. She cut off contact with Clay and later heard that he died of an overdose. Veronica has remained sober and now works for the Simington family, caring for their children.

Her old friend Lola calls with a lead on Dominic. Lola, who now works in the records department at the St. Louis Town Hall, found a suspicious birth certificate issued a week after Dominic vanished. The certificate is for a boy named Theodore, and his mother is listed as Naomi Paxson. Naomi’s mother, Lorraine, was an employee in that same department. Veronica decides to investigate the boy and his father, Jeremy Roth.

Veronica learns that Jeremy is a wealthy investment banker on Long Island. Believing that the police won’t take her seriously without proof, she stakes out his house. She follows Jeremy and a young boy to a park and is shocked to see that the boy is the spitting image of Clay. Convinced that he’s her son, Veronica approaches and sits on a bench nearby. As the children play, Jeremy takes a break and sits on a bench beside her. She strikes up a conversation, pretending that she finds him familiar. He introduces his son as Teddy and mentions his wife with a hint of dissatisfaction. Before leaving, Jeremy tells Veronica about a running trail in the park that he uses three mornings a week.

Determined to get closer to Jeremy, Veronica quits her job, moves into a nearby basement apartment, and finds work at a coffeehouse. About 10 days later, she goes to the running trail to orchestrate a meeting. Her attempt at running fails miserably, and she’s soon gasping for air. Jeremy finds her and offers her running advice. Claiming that his own knee is bothering him, he suggests that they walk and run in intervals together. They spend the session talking and make plans to meet for another run.

Over the next two months, Veronica and Jeremy become regular running partners. Jeremy talks constantly about Teddy but is reluctant to discuss Naomi. He eventually reveals that he only married her because of the baby; they had already broken up when she appeared with the infant and claimed that he was Jeremy’s son. This news excites Veronica, but her hopes are dashed when Jeremy adds that he insisted on a paternity test. He confirms that the test was positive, explaining that he mailed the samples himself and had the results sent directly to him. Though this seems definitive, Veronica’s intuition tells her that Teddy is Dominic.

Veronica continues running with Jeremy, admitting to herself that she’s attracted to him. One morning, she twists her ankle and falls. Jeremy carries her to a bench and tends to her injury with a wrap and ice pack from his car. In the intimate moment that follows, they kiss. Jeremy quickly pulls away, apologizing and explaining that he can’t leave Naomi for fear of what she might do to Teddy. As he walks Veronica to her car, however, they kiss once more.

Three months into their affair, Jeremy announces that he’s leaving Naomi. He has hired a top lawyer and intends to seek full custody, convinced that Teddy is unsafe with her. Jeremy asks Veronica to be patient while the divorce is underway and expresses concern for her safety should Naomi discover their relationship. Shortly after, Naomi catches them together.

With the affair now public, Jeremy decides it’s time for Veronica to meet Teddy. To win him over, Veronica decides to give him the stuffed elephant she has saved for Dominic for years, a gesture that feels like a final acceptance that she will never see her own son again. When they meet, Teddy is fearful, telling his father, “Mommy says a witch named Veronica stole you from us” (294). Horrified, Jeremy reassures Teddy that Veronica isn’t a witch and tells his son that he loves her. Reconsidering, Teddy decides that she must be a “good witch” and happily accepts the elephant.

Veronica begins receiving anonymous, threatening phone calls from a woman she assumes is Naomi, who promises to kill her. One afternoon, Jeremy asks Veronica to watch Teddy until he gets home from work. While they play, Veronica is again struck by Teddy’s strong resemblance to Clay. Unable to shake her doubts, she uses a DNA test kit she has been carrying in her purse. She tells Teddy that it’s a game and swabs his cheek, making him promise to keep it a secret before planning to mail the sample.

That night, Veronica receives another threatening call, this time from an unblocked number. Jeremy is with her and asks who called. Veronica finally tells him about the threats. He becomes furious and shows her a photograph of the stuffed elephant she gave Teddy; Naomi stabbed it with a knife and covered it in red liquid. Jeremy explains that this is the kind of behavior that makes him fear for Teddy’s safety.

At Teddy’s extravagant sixth birthday party, Veronica tries to ignore that her own son’s birthday was the week before. Jeremy has forbidden Naomi from attending, but she arrives anyway. To avoid a public fight, Veronica intervenes and graciously allows her to stay. Shortly after, Veronica receives an email containing the results of the DNA test. Secluding herself in the main bedroom, she opens the report and reads that there’s a 99.9999998% probability of maternity. The test is positive: Teddy is her son, Dominic.

Reeling from the confirmation that Teddy is Dominic, Veronica concludes that Naomi must have kidnapped him and somehow falsified the paternity test to trick Jeremy. As she heads downstairs to find Jeremy, she discovers Naomi in the office, smashing the robot car that Veronica bought for Teddy’s birthday. Distraught, Veronica finds Jeremy and tells him what Naomi did, but she withholds the truth about Teddy’s identity. Enraged by Naomi’s actions, Jeremy agrees that she must leave the party. Veronica decides to wait until after Teddy’s birthday to involve the police and tell Jeremy everything.

After Naomi is arrested at the party, Veronica spends time with Teddy, overwhelmed by the knowledge that he’s her son. She finds Jeremy on the phone; he has secured a temporary order of protection against Naomi, but she has already been released from jail. Jeremy then informs Veronica that he must leave for a business trip to Boston the next day and asks if she can stay overnight with Teddy. Veronica agrees, relieved to have a day with her son before she must reveal the truth to Jeremy upon his return. She promises Jeremy that she will protect Teddy with her life.