The following version of the book was used to create this study guide: Pixley, Marcella. Trowbridge Road. Candlewick Press, Somerville Massachusetts, 2020. Kindle AZW file.

June Jordan, known to family and friends as June Bug, lives on Trowbridge Road with her mother, Angela. Her father Marty died of AIDS. Angela, who has always struggled with mental illness, has developed an unrelenting, manic fear of contracting AIDS. She imagines that anything from outside might bring a terrible disease. She counters by cleaning obsessively, and nothing is safe from her efforts. After she cleans the kitchen, she cleans the items she used for cleaning. When June arrives home after playing outside, Angela is horrified and forces her to bathe in scalding-hot bleach water, scrubbing with a hard-bristled brush to get rid of any germs she might be carrying. This ritual is so harsh that June develops scars. To avoid the ritual, June packs a backpack with items that will help her clean up before she goes home, including mouthwash, alcohol, tweezers, a carrot peeler, and a letter opener. This backpack represents June's ability to have some fun outside without facing the horror of Angela's punishment afterward.

June often sits in a beech tree on Trowbridge Road,. From the tree, she sees Ziggy Karlo when he arrives to stay with his grandmother, Nana Jean. When Ziggy's mother, Jenny, drops him off at Nana Jean's, Ziggy does not want to be separated from Jenny. Jenny has decided that staying with his grandmother is best for Ziggy because Jenny's boyfriend is sometimes abusive. June pretends she is part of Nana Jean's family, being cared for by an adult who is capable of doing so. She is unaware that Ziggy sees her until she finds him waiting for her in the tree one day.

Ziggy has had hardships of his own because of his upbringing with a mother who is sometimes neglectful. Additionally, he does not conform to what his peers consider normal. Ziggy has long hair and an eclectic taste in clothes, and he is highly imaginative. What June and Ziggy discover is that their imaginations mesh immediately. Combined with the harsh home life each has experienced, they become immediate friends – a first for each of them.

Ziggy introduces June to the ninth dimension, a place where magic is real and their imaginations come to life. June leads Ziggy to a field her family owns, and they declare it the perfect place for the ninth dimension. An old cellar becomes Majestica, and June and Ziggy share adventures that include Ziggy's ferret Matthew along with an array of magical beings they conjure to life.

June's Uncle Toby knows there are problems at June's house but does not know the extent until he forces Angela to face him one day. Seeing how much weight she has lost, he insists she eat a sandwich. June sides with Toby, and she leaves soon after Toby leaves. She returns after playing with Ziggy to find that Angela has vomited up the sandwich, certain it was infected with AIDS. June cleans up the mess with the exception of Angela's clothes. Finally, she decides to bury them. She cries out her fears and frustrations as she digs. Jenny joins her, recognizing that June needs comfort. June knows Angela will force her into a bleach-water bath if she goes inside after digging in the ground. She decides that she will never go back home. Jenny takes her to Nana Jean's house. Eventually, June tells them everything. Nana Jean promises they will do what is right for June, though she is not yet certain what that is.

June and Ziggy are playing in the ninth dimension when they smell smoke. Having been dragons just a short time earlier, June fears she caused the fire . The children hide in the cellar. When Toby finds them, June learns that Nana Jean had called Angela, saying June would not be returning home right away. Nana Jean says Angela seemed relieved, but the Jordan's house burned a short time later. Angela has been taken to the hospital where she will get the treatment she needs. June stays with Nana Jean for a few days while Toby finds an apartment nearby. He moves June in with him, pledging they will always be there for each other. Jenny, meanwhile, has come to the conclusion that her abusive boyfriend is never going to change. She agrees to move in with Nana Jean. Ziggy will now be living on Trowbridge Road. He and June can continue their friendship.