Josephina "Joey" Vasquez is a thirty-two-year-old corporate lawyer in Los Angeles who has spent most of her adult life quietly unhappy. She is secretly in love with her best friend, Elijah "Ellie" Aarons, who married another woman, Cat, seven years earlier. Joey's closest companion is Ruthie, her rescue cat.
One November evening in 2026, Joey attends a dinner party at Ellie and Cat's home. She is blindsided by the presence of Alex Aquino, a near-billionaire tech figure she has not spoken to since a one-night stand at Ellie's wedding. Joey suspects Cat is pregnant, a realization that sharpens her grief over the life with Ellie she will never have. She leaves in tears, and driving home on the freeway, distracted and emotional, she crashes into a truck and dies.
Joey regains consciousness in a retro 1970s-style office. A stern caseworker informs her she died and that her file indicates extensive regrets. The caseworker offers a second chance: Joey can return to any earlier point in her life with all her memories intact, but she must tell no one or her existence will be erased. This is her only do-over. Overwhelmed with grief for Ruthie, Joey accepts. When asked when her regrets began, she blurts out "my first college party" before she can clarify she was just thinking aloud, and she is immediately transported.
Joey arrives at a frat party in September 2012, eighteen years old again. She steers her roommate, Madison James, away from Jake, the toxic boyfriend who consumed three years of Madison's life, and redirects her toward Patrick Leon, Ellie's best friend. Joey recreates her first meeting with Ellie but this time kisses him and leads him upstairs. They sleep together. He never calls. Joey watches Ellie gravitate toward Cat and realizes that by sleeping with him on their first night, she changed their dynamic: Instead of becoming her best friend, Ellie now sees her as a one-night stand.
Meanwhile, Joey catches the scent of watermelon-flavored vapor outside her dorm and finds eighteen-year-old Alex reading at a picnic table. Their combative banter sparks an unexpected connection. Over dinner, Alex opens up about his father, who had a gambling addiction and repeatedly abandoned his family, and Joey shares her anxieties about her mother's exacting expectations. Alex tells her that her life is hers to live. They kiss goodnight, and Joey agrees to a date, telling herself Alex is only a distraction from Ellie.
Motivated by Alex's advice, Joey drops her pre-law courses and enrolls in film, creative writing, and art classes, investing her savings in Bitcoin based on her knowledge of its future value. In creative writing, she meets Helen Cohen, a quiet classmate whom Joey knows will die of a heroin overdose at twenty-seven in the original timeline. Joey resolves to befriend Helen and prevent that fate.
Joey and Alex's relationship deepens through a series of dates. They bond over their shared Mexican heritage, and Alex responds with patience when Joey has a panic attack on the highway triggered by her fatal accident. A flashback chapter reveals what happened at Ellie's wedding in 2019: Joey sneaked out heartbroken, found Alex vaping by the dumpsters, and they ended up at her apartment. The next morning, she overheard Alex telling his wife, Ingrid, "I love you too" on the phone. Joey blocked his number for seven years.
Back in 2012, Joey discovers Second Take Anonymous, a support group for people living their second lives. Members debate whether Joey can save Helen and suspect that anyone who confessed the truth to outsiders was erased, leaving only a nagging sense of absence at meetings. Joey also gets a job at the West Los Angeles Animal Shelter, hoping to find Ruthie as a kitten, but does not locate her.
As the semester progresses, Joey's creative writing stories, plagiarized from future films, impress her classmates. When she falls ill, Alex arrives with soup and medicine, caring for her so tenderly that she realizes he is no longer just a distraction. But the situation with Madison explodes when Joey discovers Ellie wrote a thinly veiled, unflattering story about their hookup for class workshop. Madison emerges from Ellie's room, revealing she has been secretly dating him, and accuses Joey of neglecting their friendship all semester. Devastated, Joey turns to Kimiko, a former ballerina and fellow second-lifer, who advises her to stop orchestrating her life around old relationships.
Joey asks Alex to be her boyfriend, and he accepts. They sleep together, and Joey realizes she is in love. At Thanksgiving in San Diego, she tells her mother she will not go to law school, triggering a family blowup during which her older sister, Sierra, reveals she never wanted to be a doctor and only pursued medicine to please their parents. The honesty opens space for a better relationship between the sisters.
At an End of the World party on December 20, Ellie apologizes for his story and asks Joey to help him reconcile with Madison. Joey feels nothing romantic for Ellie, confirming their chapter is over. But Alex witnesses their hug and storms out. When Joey chases him, Alex accidentally reveals he is also living his second life, saying he had "decades" to accept that Joey would always choose Ellie. He confirms his caseworker showed him Joey already in her second life and sent him to the exact moment of their first dinner together.
A chapter from Alex's perspective fills in his story: After Joey died in 2026, he adopted Ruthie and spent seven years with the cat before developing lung cancer and dying at fifty-eight. Offered a second chance, he told his caseworker he wanted to make Joey fall in love with him. The caseworker, breaking protocol, showed him Joey on a screen already living her second life and calculated the optimal moment for his return.
Joey breaks up with Alex, feeling that every moment between them was calculated. She returns to her dorm and reconciles with Madison. During winter break, Sierra switches from surgery to pediatrics, and Joey gets a prescription for antidepressants. Back at the shelter, planning to quit, she discovers two kittens who arrived on New Year's Eve: a gray tabby named Penguin and a tortoiseshell matching Ruthie's description exactly. Diego, the shelter employee Joey befriended months earlier, explains the bonded siblings were found in a dumpster by the beach. Joey adopts them both and, after reconciling with Kimiko, arranges for Kimiko to house the cats in her apartment.
Alex comes to the dorm to apologize. When Ruthie, who has been hiding under Joey's bed for days, emerges for the first time and approaches him, Alex begins to cry. He reveals he adopted Ruthie after Joey's death and spent seven years with her. Joey watches his unguarded grief and recognizes that nothing is artificial in a man weeping over a cat. She tells him they can try again with no lies between them and confesses she is in love with him.
The epilogue jumps forward four years. Joey, Alex, Madison, Ellie, Patrick, Helen, and Kimiko vacation together in Thailand, with Sierra cat-sitting Ruthie and Penguin back home. Joey plans to become a therapist for people living second lives, inspired by the absence she senses at Second Take Anonymous meetings. Alex has grown wealthy again through investments, a trait Joey has accepted as fundamental to who he is. She reflects that they literally had to die to find each other, but she would not trade their messy love story for anything.