Thirteen-year-old Zinnia Taylor lives in a rambunctious household. Three brothers and three sisters, all of whom seem to have a noisy way about them, push Zinny through the "dog trot" passage into the quiet sanctuary of the home of her Uncle Nate and Aunt Jessie and cousin Rose. Zinny and Rose are the same age, and she comes to think of Uncle Nate and Aunt Jessie as her second parents. Here Zinny is one of two children until the age of four when she gets whooping cough. Rose gets whooping cough, too, and dies. Aunt Jessie changes after her daughter's death and seems to live in a dream world.

When Aunt Jessie dies, Zinny begins to think that both deaths were her fault and takes on a burden of guilt. She is certain Rose caught whooping cough from her and that she has frightened Aunt Jessie so badly with a snake that she died. Following his wife's death, Uncle Nate's mental condition deteriorates. He chases shadows and mists, certain he is seeing Jessie, saying he is chasing his Redbird, his nickname for her.

Then Zinny's best friend moves away, and she is left with too many siblings, too much noise, and too little room. The discovery of an old trail overgrown with grass and weeds provides the perfect project for her to be alone to sort out her feelings of guilt at being a "murderer." She believes the trail is hers and no one else's and becomes obsessed with clearing the trail, all twenty miles of it, and planting zinnia seeds the full length. Zinny says,

At the time, I thought this idea dropped down out of the blue, and I didn't know it would become so important. It didn't occur to me that I might be escaping something or even chasing something. It didn't occur to me that it would seem selfish. As for the zinnias and naming the trail after myself—well, I suppose I wanted to be known as something other than the strangest and stingiest dirt-daubing doodlebug, as something more than a little mashed-up fritter at the bottom of the pot. I suppose I wanted people to know exactly which Taylor I was, and for me to be something other than "Zinnia Taylor: killer."

Uncle Jake tries to dissuade her and she wonders why he does not want her up on the trail. Was he meeting someone up there, and he did not want anyone to know?

Besides the voids created by her losses, there is Jake Boone, recently returned to Bybanks, Kentucky, with his mother. Jake clerks at Mrs. Flint's general store and develops a special interest in Zinny. He begins giving her gifts, starting with cookies at the store, a hundred bottle caps, a stolen dog, a cricket, a small carved horse, and, ultimately, his mother's ruby and diamond ring. Zinny is suspicious of his intentions. Other boys have befriended her when they really were interested in her older sisters, especially, May. Zinny is not about to be made a fool of again, especially when May already wants to be Jake's girlfriend.

Zinny gains permission from her parents to clear the trail and sets about the task with a niggling sense of mystery as she uncovers stone after stone on the trail. She has plenty of time to think about her family, Jake, Uncle Nate, Aunt Jessie, and Cousin Rose. By the time school is out she has cleared four miles, but those miles start stretching out when she devotes each day to clearing the trail. She finally progresses so far that it takes too much time to walk to the end each morning and back home in the evening, so she convinces her parents that she should be allowed to camp along the trail. They insist on some conditions to insure her safety, and she agrees to come home every ten days.

Time stretches out before Zinny as she sets up camp and works on the trail. She encounters some unsavory characters one evening, and sometime later she stumbles into the path of a bear.

There was another source of unease, more difficult to explain. Several times I glimpsed a fluttering at the corner of my sight, or a moving shadow, or a spot of color—often red—as of someone's sleeve or cap, ducking behind a tree. I'd halt, wait, listen, suspecting that someone was near, watching me, spying on me. Sometimes I thought it was Aunt Jessie I was seeing, and that she was there in the woods, watching over me.

Small items that make life a little easier appear in her camp site. She is fortified and reassured by her Dad's "visits" when he hitches rides with the pilot of a crop duster and keeps watch on her and her progress.

When day ten arrives and she heads home, she is surprised by her own eagerness to go home. She is not sure whether she should stay the night or just grace them with her presence for a few minutes. She thinks they might be happier with her gone and annoyed if she comes back and gets in everyone's way. On her way down the hill she sees Jake Boone on the trail and calls out to him. Then she discovers that he has been "watching over" her as he puts it, and that he was the one responsible for the sudden appearance of the items she had forgotten. She is annoyed with him for "protecting her" and annoyed with herself for sounding nasty. She is happy that he had wanted to protect her but suffers conflicting feelings and emotions she cannot understand.

Zinny's quick thinking saves her from harm when she meets two teenage boys who are drinking and hunting. A mother bear and her cub become a metaphor for Zinny when she thinks of the times Aunt Jessie stepped in between Zinny and her mother. She had always thought her mother did not care, but maybe Zinny was wrong, maybe her mother had been angry like the bear. Tired and hungry, Zinny wants to sleep but slips and falls from the tree where she has taken refuge from the angry bear. In a tired and demented state she follows Aunt Jessie out of the woods to a clearing. Zinny lies down in the clearing and sleeps till daybreak then finds a cabin. She looks through a crack in the shuttered windows and sees Aunt Jessie's coat. The joy and horror of seeing the coat propels her down the hill to the pasture where she cuts a fence, mounts a horse pastured there, and rides for home. Her family is leaving for the circus, and she stays behind to look after Uncle Nate. After they are gone, she puts him on the horse and takes him to the cabin, where the mystery unraveled.

Zinny and Jake discover they like each other, and a meaningful friendship develops. The zinnias grow and bloom along the trail, and visitors follow the trail and find Zinny's house. In the end, the whole family loses their privacy as strangers start using the trail. "One day two women clomped onto the porch, asking to use the bathroom. "There's no facilities on that trail,' they said."