Willow Chance is introverted and a genius. She obsesses over two things: plants and medical conditions. Her adoptive parents have allowed her to build an incredible sanctuary of plants in their backyard. They also have her transferred to a different school in the hope that Willow can find a teacher to challenge her. They also hope that she will finally make a friend.
Willow is suspected of cheating on a standardized test because she finished it perfectly and in just a few minutes. She is sent to receive counseling from Dell Duke, a man who never wanted to become a school counselor and is not quite sure how to do his job. Dell has his own method of labeling the kids he counsels into categories such a loners and weirdos, but he soon realizes that Willow is in a category all her own. She is a genius, and he wants to get her know her better in hopes of exploiting her intelligence for his own benefit.
Willow makes her first friend in Dell’s office. Nguyen Thi Mai is two years older and accompanies her younger brother, Quang-ha, to his counseling sessions. Willow is immediately drawn to Mai and begins to learn Vietnamese so she can communicate with her without Dell understanding them.
Willow wants to reach Dell’s office early so she will have time to talk with Mai, so she begins taking a taxi to her meetings. The first time she does this, she asks for the driver’s papers. Jairo Hernandez, the driver, thinks she may be some kind of undercover agent. But when Willow steps out of the cab and gives him some sage advice, Jairo sees her as a kind of angel.
He begins to think about going back to school so he can become more than a taxi driver. The following week, Willow requests Jairo specifically from the taxi service. He has cut his hair, and Willow notices a mole on the back of his neck. Willow writes a note telling him to go at once to a doctor and have a biopsy performed on the mole.
That afternoon, Dell takes Willow, Mai and Quang-ha for ice cream. When he arrives at Willow’s house to drop her off, they find a police car parked in the driveway. Willow’s parents have been killed in a car accident.
Mai convinces the police that she and her family have been close friends with the Chances for years so Willow can stay at their home for the night. Mai’s mother, Pattie, owns and runs a nail salon. She escaped Vietnam when she married an American serviceman, who later abandoned her and their children.
Pattie recognizes the grief in Willow’s eyes and agrees to take custody of her for the night. The family lives in the garage behind the nail salon. The children must share a queen-sized mattress on the floor. Pattie cooks dinner with two hot plates and a microwave.
The following afternoon, Willow is taken to an emergency foster care facility. She sees a newspaper with a picture of her parents’ demolished truck. She passes out and hits her head. After receiving nine stitches, Willow evades the social worker and sneaks away from the hospital. She calls the taxi service and asks again for Jairo.
When he arrives, she explains that she cannot pay him, but will get money to him soon. He tells her she does not need to pay. He considers Willow his guardian angel, as he had his mole removed just that morning and the doctor told him it looked cancerous.
Willow asks him to drop her off at the library where she takes refuge in a corner behind a large chair. She soon falls asleep. The police call Dell and ask for his help in finding her. Dell takes Mai out of school, and she guides him to the library and Willow. Before they head back to the authorities, Mai comes up with a plan.
She convinces Dell to let her mother put down his address as their own. Then Willow can stay with the Nguyens in their garage until the social worker can find a proper home for her. Dell is supposed to supervise her home schooling until she feels up to returning to public school.
The plan goes well for a month, but then the social worker requests a home visit. In a panic, Pattie calls Dell and convinces him to let them pretend to live there. Unfortunately, Dell has lived as a hermit. His home is furnished with lawn furniture, and he sleeps in a sleeping bag on a mattress. Pattie and her children buy furniture and cooking utensils from a thrift store. Then they clean and scrub the place until it sparkles. After they pass the inspection, Pattie suggests the family stay in the apartment since there will be several more home visits until Willow is placed in a proper foster home.
Dell reluctantly agrees. He moves in with a neighbor in the complex, and Pattie takes over his bedroom. The girls share a room and Quang-ha sleeps on the couch. Dell eats dinner with them and watches television with Quang-ha.
Mai and Quang-ha are thrilled to be in an actual apartment. Dell finds himself losing weight because he is eating better. He starts jogging to get in better shape. At the same time, Willow begins to engage in life again.
Willow does not return to school, but she helps Quang-ha with his homework. She does such a good job writing his papers that he is put into an honors English program. Willow also helps Pattie rearrange her nail salon so they can add another technician and still have room to maneuver. She also shows Pattie the best disinfectants to use, and the rules the technicians should follow to avoid infections.
When they post a sign proclaiming their standards, new clients start pouring into the spa. Although their apartment complex is called Gardens of Glenwood, there is no garden. Willow begins a campaign to create a sunflower garden. She gets Dell and the Nguyens to help her plant various sunflower seeds in pots to start them growing. She then creates a binder filled with facts and plans.
Dell goes to the bank that owns the complex to gain their approval for a garden. Willow’s binder impresses the bank. They grant permission and make Dell the building representative. He is thrilled to be given such authority. Willow and her friends plant the flowers and, in the process, make even more friends in the complex.
Jairo decides to return to school. While buying his books at the store, he is shocked by a swirling light and buzzer. He is the one-millionth customer and wins $20,000. It is a year’s salary for him. After he drives Willow on an errand, he stops at the salon so Pattie can meet him. She gives him her phone number in case he ever needs to talk to her.
Willow finds this strange and realizes that Jairo is the first person Pattie has not tried to boss around. Jairo tells Willow about his good fortune in winning the money and how he will go back to college.
A court date is set for a judge to decide if Willow should be placed in a long-term foster facility. Meanwhile, her sunflowers have bloomed and will soon die. She decides to plant a more permanent garden in the courtyard. She talks to a friend at the local nursery. The following day he comes with a large truck filled with trees and plants for Willow’s garden. Another friend donates solar lights to illuminate the garden at night.
Willow’s court date arrives, and she reluctantly goes with the social worker. She is surprised when she is called to see the judge in her chambers. Inside is Willow’s new family: Mai, Quang-ha, Pattie, Dell and Jairo. Pattie and Jairo have asked to have guardianship of Willow. Pattie and Jairo have begun a relationship.
Also, Pattie has been hoarding money. She is quite wealthy. She has made an offer to the bank to buy the Garden of Glenwood apartment building. Willow leaves the courthouse in the company of those she has come to love. Her new, wonderful family is made up of broken, caring people. She will never stop loving and missing her parents, but she is ready to restart her life.