The following version of the book was used to create this study guide: Yang, Kelly. Three Keys. Scholastic, New York, NY, 10012. 2020. Kindle AZW file.

Three Keys is the second installment of the Front Desk series narrated by 11-year-old Mia Tang. Mia and her parents immigrated to America from China several years earlier, and Mia is just settling into a new year at the local school along with her best friend Lupe Garcia. Mia and Lupe wind up in Mrs. Welch's class, and Mia is immediately annoyed that Mrs. Welch speaks out in favor of stricter immigration laws. She also stricter than Mia's previous teacher. The mediocre grades make Mia question her dream of becoming a writer. While Lupe and Mia are settling into their new class, a Chinese student named Jason Yao is upset that he has been placed in a different class. Mia considered Jason to be her nemesis the previous year, but Jason is now working hard to spend time with Mia and her friends. When Jason reveals that the kids in his class make fun of him, Mia realizes that Jason really needs a friend.

Mrs. Welch often leads the students in discussions about current events, including the governor's race and Proposition 187 that would make tougher immigration laws. If passed, the law would eliminate public education for illegal immigrants, including Lupe. Mia knows many immigrants who are in America legally and some who are not. She feels that everyone should have the right to build a better life. When Lupe's maternal grandmother dies in Mexico, Lupe's mother makes the trip home for the funeral despite the concern she may not be allowed to cross back into America. Mrs. Garcia finally telephones home with the news she has found a coyote, meaning a person who is paid to help people cross the border illegally. Days pass, and Mrs. Garcia does not return home. When Lupe's father Jose goes to search for her, immigration police arrest him and threaten deportation. Mia, Lupe, and their friends quickly begin working to free Jose. They find a lawyer who offers to take on the case for free, create petitions, and write many letters. One of Mia's letters is published as a letter to the editor in the local newspaper.

While Mia is dealing with all these issues, her relationship with Mrs. Welch continues to spiral downward. One day, Mrs. Welch has Mia help clean the classroom as punishment. Mia discovers a framed diploma and learns that Mrs. Welch has a Ph. D. Ying tells Mia this is the most difficult degree to obtain. It qualifies Mrs. Welch to teach college. When Mia and Mrs. Welch have a heartfelt talk about the fact that not everyone is able to follow their dreams, Mrs. Welch offers to tutor Mia to improve her writing. Mia is soon more confident that she will become a writer. She continues to help her friends, encourages Jason to follow his own dreams. She is pleased when it seems Ying might become a teacher.