An hour-old baby, abandoned on a street corner without even a blanket, was found with a scrap of paper reading, "Call her Hollis Woods." Hollis is eleven now and has been in foster homes all her life; she does not stay at any of them for very long. All of these places run together in her mind except the last one, the Regans' summer home in Branches, in upstate New York. It is October now, and she rides to a new placement with her social worker, a lady she calls "the mustard woman" because of a stain on her sweatsuit. Hollis is a gifted artist, and she thinks about the pictures she has created, especially a representation of a family she had done for a school assignment when she was only six. The assignment had been to find a picture of something beginning with the letter W, and Hollis's teacher had said she did it wrong because family starts with F. She had not stayed to hear Hollis explain that the picture did stand for something starting with W: it showed her dearest wish.

Hollis is placed Josie Cahill, a retired art teacher who is "movie-star beautiful," albeit a little eccentric. Josie carves tree branch figures and promises to make one of Hollis, if she decides to stay. Josie sometimes forgets that Hollis should be in school, which is fine with Hollis, who spends her time in the classroom sitting unnoticed in the back anyway, drawing. Josie takes Hollis on adventures to the ocean and to the movies in town, where they pay for their admission by selling popcorn. Josie's "best lifetime friend," Beatrice Gilcrest, works the theater ticket counter, and on Monday nights she comes to visit at Josie's house and brings Chinese food for dinner. Beatrice is amazed when Hollis allows her to see her drawings, observing, "I never saw anyone who was able to do this . . . and I was an art teacher for forty years." Someone else had told Hollis a something similar once: Steven Regan and his parents, Izzy and the Old Man, had recognized her talent as "a gift, pure and simple." Hollis had been happy with them, and they had loved her unconditionally, but then something happened and she had to go away.

Josie senses that Hollis is going to stay with her for a while, so she begins carving her likeness in wood. The mustard woman comes by the house to check up on Hollis and is dismayed to find her down by the pier with Josie when she should be in school. Josie is slowly sinking into dementia, and Hollis knows that if the mustard woman discovers the truth she will not be allowed to stay. In early December, Beatrice relocates to New Mexico and tells Hollis to take care of Josie, and leaving her phone number "just in case." One morning, Hollis misses school again, opting to go to the pier instead. When she returns, the mustard woman is there talking to Josie, and Hollis perceives that Josie does not know who she is. The mustard woman tells Hollis that she has found a new family for her. She will be coming by on Saturday to take Hollis to them.

Knowing that Josie cannot stay alone, Hollis is frantic. She tries to call Beatrice, but Beatrice cannot be reached. All Hollis can think of is the summer house in Branches where she lived with the Regans; images of her last weekend there come flooding back, inspired by the drawings she keeps. Steven, Izzy, and the Old Man had wanted to adopt her, but the Old Man and Steven had always seemed to be arguing, and Hollis had been sure it must have been because of her. Then, after what had happened on that last fateful weekend, she had known beyond a doubt that she could not stay. Now, though, the summer house at Branches should be empty; Josie can still drive, and there is a map in the glove compartment of the old Silver Bullet in the garage. With Hollis gently guiding, Josie takes them the long miles to their destination. The Old Man's mountain stands tall in the background, there are "a million stars" overhead, and the house is beautiful in the snow. Hollis breaks a window to get in, starts a fire, and settles Josie cosily before it. She then maneuvers the Silver Bullet into the shed, next to the crushed remains of a pickup truck.

Hollis has brought provisions enough to sustain herself and Josie for a while. She is frightened when she sees a fisherman on the far side of the river and when she hears the drone of an engine nearby; it is important that their presence not be detected. As Christmas approaches, Hollis and Josie joke about Santa coming to visit on a sleigh; Josie says that a sleigh is old-fashioned and that now Santa comes on a snowmobile. Josie spends her time working on Hollis's carving, and Hollis draws pictures of their beautiful surroundings. The Old Man's mountain reminds Hollis of her last weekend with the Regans. Izzy and the Old Man had gone to town, and Steven had gone fishing. Hollis had taken the time alone to do something she had always wanted to do: climb to the top of the Old Man's mountain, "three hours up, and three hours back, a cinch." At the top of the mountain, she had danced with joy, her dream of a family almost realized. Stepping too close to the edge, she had taken a fall. She knew she would never be able to walk all the way back down alone. Just before sunset, Steven had come at the wheel of the pickup that he was too young to drive. As they went down the mountain, the truck had started to slide, careening out of control and flipping over the edge. When it finally stopped rolling, Hollis had crawled out and gone to get help for Steven, who was hurt badly. Hollis had been patched up and taken home to rest while Izzy and the Old Man waited at the hospital for Steven. Hollis had known that Steven had driven up the mountain because of her. Convinced that she had "messed up the whole family," she had run away.

Hollis thought she knew where everything was in the summer house, but on Christmas Eve, Josie gleefully surprises her with pancake mix, a jar of applesauce, and a box of dried milk. On Christmas morning, Hollis gives Josie a picture of her and Beatrice as they must have looked when they were young. Josie has presents for Hollis too: a tin of Izzy's candy and the tree-figure carving she has been working on of Hollis. Later, in her room, Hollis spreads her drawings out on the bed. She sees that Josie is not happy at the summer house in Branches, and she knows what she must do. She will call Beatrice, and Josie will go back home, where she longs to be. Hollis will burn all the drawings of herself and the Regans and put them out of her mind forever, then go on to live in yet another place. Before she destroys the pictures, however, Hollis studies them one more time. She remembers that the Old Man had come to see her after the accident, after she had run away and been caught. He told her that they, the Regans, all loved her, that the accident wasn't her fault, and that they still wanted to adopt her. But Hollis had been "tough" and refused to listen. She thought that now the Old Man, who had always argued with Steven, was blaming him for the accident instead of her. Hollis had been sure that she really was ruining the family; she could never go back. As she looks at the pictures now, though, Hollis sees things she had never realized were there. There is one of Steven fishing, and the Old Man is smiling at him. In another, Steven and the Old Man were laughing in a boat. Hollis wonders how she could have drawn it but never really seen it: "of course the Old Man loved Steven," he would love him whether Hollis was there or not.

Hollis suspects something else, too, about the sound of the engine and the food and candy Josie "found." She sets out to walk the four miles to a pay phone to call Beatrice, and she hears a snowmobile; it is Steven, who has been watching over her all the time she has been at the summer house. The Regans had been informed that Hollis was missing by the adoption agency, and Steven had known immediately where she would go. Steven asks Hollis about the one thing he cannot comprehend, why she will not accept the home the Regans want to share with her. Hollis tells him how she thought she "messed up the family," and Steven, amazed, says that the accident really was his fault and that he and the Old Man argue because "it's just the way we are." Steven tells Hollis that she is misunderstanding, putting all the blame on herself because, having never had one, she "just [doesn't] know about families yet." Beatrice comes back to take care of Josie, and Hollis goes home, to live with the family that loves her. A year and a half later, the Regans go to visit Josie and Beatrice at the house by the ocean. There are five of them now: Izzy and the Old Man, Steven, Hollis, and Christina, the new baby sister.