Twelve years after losing her husband in a car accident, Kate Waithman, a music therapist in New York City, is still struggling to move forward. The novel opens with Kate's memory of her last night with Patrick, her husband of four months. He arrived home late after meeting his ex-girlfriend, Candice Belazar, claiming she had something important to tell him. Kate went to bed angry before he could explain. The next morning, they reconciled, and Patrick gave her a silver dollar, part of a family tradition of returning coins to the universe when something good happens. He promised big news at dinner, then left for work and never came home: A drunk driver crashed into his taxi near Times Square, killing him.
In the present, Kate specializes in working with children with special needs and has recently learned she has primary infertility. She confides in her best friend, Gina, whose husband died in the September 11 attacks. Kate is dating Dan, a polished man whom everyone considers perfect for her. When Dan proposes publicly, Kate says yes despite a fleeting hesitation. Dan reacts with relief, saying they do not need children, and deflects when Kate mentions adoption. Patrick's mother, Joan, tells Kate that Patrick would want her to be happy.
The morning after the party, Kate wakes in her old apartment on Chambers Street beside Patrick, alive and in his early forties with thinning hair at the temples. The room glows with saturated colors and dreamlike light. Kate recognizes details she should not know: a Dyson vacuum, a Word-of-the-Day calendar, yellow roses. When she questions the experience, the world flickers; when she accepts it, everything sharpens. A girl appears in the doorway, about twelve years old with green eyes exactly like Patrick's. She calls Kate "Mom," but the dream dissolves before Kate can learn more.
In real life, Kate confirms with her sister Susan that Susan's husband, Robert, did receive a job offer in San Diego the year after Patrick died. Susan insists Kate must have overheard this at some point. Kate visits her old building and finds a playground where a funeral home once stood, exactly as she saw in the dream.
In her second dream, Kate learns the girl's name is Hannah. Hannah has cochlear implants and communicates using a mix of spoken English and American Sign Language (ASL). Kate can understand Hannah's signing but cannot sign back, and her inability disrupts the dream. She wakes to find that a cut from the dream has appeared as a real wound on her hand. Doctors attribute it to sleepwalking.
Determined to communicate with Hannah, Kate enrolls in an ASL class taught by Andrew Henson, who supervises deaf and hard-of-hearing foster children at St. Anne's Services in Queens. Andrew learned ASL because his younger brother Kevin was born hard of hearing. Kevin was killed at nine when he did not hear a car approaching, and the loss led Andrew to social work. Andrew invites Kate to volunteer as a music therapist with his foster children.
Kate begins volunteering at St. Anne's, where she bonds with Allie Valcher, a twelve-year-old piano prodigy with cochlear implants whose mother is working to regain custody after drug arrests. Kate connects with Allie through music, and Allie opens up about her mother and her best friend Bella, a deaf pianist and fellow foster child.
In subsequent dreams, Kate attends Hannah's piano recital, where Hannah removes her cochlear implant processors to perform a Beethoven sonata. Joan appears gaunt and bald from cancer treatment, prompting Kate to check on the real Joan. In another dream, Kate discovers that in the alternate world, Andrew's brother Kevin survived and Andrew never became a social worker. She realizes the dream world, despite its beauty, lacks something essential: The growth that came from grief shaped both her and Andrew into who they are.
Kate's relationship with Dan erodes over unresolved disagreements about children. After a dream in which Patrick tells her she is a wonderful mother, Kate ends the engagement, explaining that they have been living on the surface. Dan accuses her of being obsessed with her dead husband and leaves.
Kate decides to become a foster parent, hoping to provide a home for Allie, and Andrew eventually supports her despite initial reservations. She completes parenting courses, passes a home study, and is certified on September 18, the twelfth anniversary of Patrick's death. She rushes to St. Anne's expecting to be matched with Allie, only to learn a judge has returned Allie to her mother. Kate is devastated. Andrew suggests Allie was meant to show Kate her capacity to make a difference rather than to be hers permanently.
Kate spirals briefly before Andrew shows up at her apartment, telling her that honesty suits her and she should speak her mind more often. Kate visits Joan and learns Joan has stage 3 breast cancer, confirming what the dreams showed. She insists Joan move in for treatment. While clearing the guest room, Kate finds a chest Patrick gave her when he proposed, filled with reasons he loved her. The last expresses his wish to have children with her and his belief she will be an amazing mother. A silver dollar falls from the closet shelf, and Kate throws it into the East River, returning her good luck to the universe.
Encouraged by Gina, Kate calls Andrew and asks him on a date. He reveals he has been interested in her, and they agree to go out.
Days later, Allie arrives at Kate's office in a panic. Her best friend Bella, whose real name is Hannah Belazar, is a thirteen-year-old deaf pianist who recently discovered her birth mother is alive. Kate and Allie rush to the bar where the mother works and find Candice Belazar approaching the entrance. Candice reveals that Hannah is Patrick's biological daughter. She hid the pregnancy until Hannah was fourteen months old and diagnosed as deaf, then told Patrick and asked him to take the child. Patrick was overjoyed and planned to tell Kate at dinner that night, the night he died. After Patrick's death, Candice gave Hannah to her own mother, who eventually died, sending Hannah into the foster system.
When Hannah arrives, Kate speaks the family's private phrase of love, and Hannah, without knowing why, completes it. Hannah tells Kate her grandmother said her father would have loved her if he had gotten the chance.
In the epilogue, set eight weeks later, Joan is living with Kate and undergoing chemotherapy, finding new purpose in her granddaughter. Blood tests have confirmed Hannah is Patrick's child, and adoption paperwork is underway. Kate and Andrew are dating. Hannah's belongings include a sketch of a family at Disney World, identical to one Kate saw in her dreams, and a jar of silver dollars found on streets over the years. On the night before Thanksgiving, Kate walks to the Pulitzer Fountain outside the Plaza Hotel, where she and Patrick planned to throw their silver dollar the night he died. She removes the coin from her necklace, kisses it, and tosses it into the water. In one final dream, Kate holds Patrick and tells him she will love Hannah always. She acknowledges this was the life she could have had but not the life intended for her. She is ready for the one she has.