When I was in high school, I got kicked out of the car on a family vacation, somewhere between San Francisco and L.A. They only drove a few hundred yards without me, but more than three decades later I clearly recall the terror I felt chasing the minivan down the highway.

Una Mannion's "A Crooked Tree" opens with the nightmare version of my brief childhood trauma. School's out for the summer and the Gallaghers are headed home. Ellen and her four siblings are bickering; their single mom is exhausted. After Ellen answers back one too many times, her mom stops the car, kicks her out and drives away. Ellen is 12 years old, she is five miles from home and the sun has set.

While this uneasy intro has serious consequences and drives thriller-like plot points, Mannion is not concerned only with what happens to Ellen. The main story, and what makes this debut so engaging, is the affecting portrait of adolescent uncertainty confronting the novel's narrator, Ellen's 15-year-old sister, Libby.

Frustrated by changes beyond her control, Libby envies what she sees as the "bright lives" of her peers in Valley Forge Mountain, a stratified but close-knit community west of Philadelphia's suburbs. Keg parties and awkward kisses are supplanting the comfort of her forest hideout and the illicit thrill of pilfered cigarettes. Her best friend is increasingly occupied by a summer job and a summer fling. And Wilson McVey, the 20-year-old troublemaker, keeps popping up, ostensibly to help, but instead putting Libby more on edge.

Things at home aren't any better. Her punk rocker big sister has graduated and is moving to nearby Philly. Her mom is still dating the man she divorced Libby's father for, but "even though [he's] been around for years" and was "obviously" the father of Beatrice, the youngest Gallagher child, Libby has never met him. And Libby's father, dead less than two years, remains at the forefront of her thoughts, both in their shared love of trees and in her memories of their vacations to his childhood home in Ireland.

Much of the conflict is due to Libby withholding information, which can be a lazy narrative device, but given how well Mannion captures all that Libby is trying to cope with — fears, insecurities, mood swings, rash lashing out — it generally works fine.

"A Crooked Tree" is particularly welcome at the end of an exhausting year when so many of us have become inextricably linked to technology. It takes place in 1981, when computer screens and cable TV were in their infancy, and kids roamed outside all summer long, from dawn till long past dusk. It's a coming-of-age tale with the heart of a serious thriller and some YA/after-school-special lessons tossed in. Put simply, it's a good story told by a smooth, genuine writer. In a time when so many of us would like nothing more than a bit of escape, those qualities are incredibly appealing.

Cory Oldweiler is a freelance writer and editor.

A Crooked Tree

By: Una Mannion.

Publisher: Harper, 320 pages, $27.99.