The following version of the book was used to create this study guide: West, Kasie, By Your Side. HarperCollins, New York, NY, 2017. Kindle AZW file.

Chapter 1 begins with Autumn's account of how she came to be locked in the library after stopping by there with friends to finish a project together. She recounts that when the group was leaving the library, she placed her bag in her friend Jeff's car trunk. Then, she went back into the library to use the bathroom. The lights went off while she was in the bathroom. When she walked out into the library and tried to leave, she discovered the library door was locked. She was not worried, thinking that someone would soon discover she was missing and return for her. But, her friends all assumed she was somewhere else because Autumn has a habit of distancing herself without notice at odd moments. Her friends do not know that Autumn is coping with extreme anxiety, kept mainly in check with medication. Undoubtedly, her anxiety is a problem in many situations. She has hidden her illness from her friends, fearing that they would treat her differently.

Autumn's anxiety rises in the locked library when she discovers that she is not there alone. Dax Miller, who has a less-than-stellar reputation at school and is a mystery to Autumn, is locked in with her. Though Autumn knows little about Dax other than the rumors, she is relieved for the company. Friday night passes without anyone coming back for her. Autumn decides to pass the time with Dax. With no other way to reach out, Autumn considers pulling the fire alarm. Dax convinces her not to do it. More than likely, Dax is already in trouble. He had probably planned to spend the weekend alone in the library because he has no other place to go besides home to his foster parents.

After two nights in the library, Autumn and Dax are watching an old movie on the television when they see a news report. Autumn's friend Jeff had an accident Friday night. He is in the hospital. Everyone assumes Autumn was with him; however, she is missing and presumably dead. The report prompts a full-blown panic attack for Autumn. Dax pulls the fire alarm, summoning help.

Autumn wakes in the hospital and discovers that everyone is relieved that she was not in the car with Jeff after all. Jeff's mother believes that Autumn is important to Jeff, and she arranges for Autumn to visit Jeff while he is still in ICU. Her efforts make Jeff's best friend angry. Autumn attempts to smooth over the situation, but she feels increasingly uncomfortable with some of Jeff's friends, his mother, and her own need to take care of herself. She is also struggling with her feelings for Dax, who has basically ignored her since they returned to school. Dax makes it clear that he does not want any form of relationship, even friendship.

Eventually, Autumn has to face the fact that Jeff's outlandish ways, though attractive on a superficial level, are not good for her in a relationship. The situation comes to a head when Jeff and some of his friends stage a pretend kidnapping, dragging Autumn to a sports event at school. Even while she knows she is overreacting, her anxiety attack is very real. Finally, she has a heartfelt talk with her friends, including Jeff, who are more understanding than she had imagined. She and Jeff realize that their flirtation is not actually going anywhere, and they agree to be just friends. She manages a moment alone with Dax who finally admits that he is drawn to Autumn and is ready to face his own fears about commitment. As the novel comes to a close, Autumn and Dax attend a party together with Dax providing the emotional support Autumn needs to get through an evening that might otherwise be overly taxing. Autumn realizes that her friends are still behind her, even though they now know the truth.