After eight months as a captive in a Utah “treatment” centre, the young teenage girl grabbed her chance to escape. At 4:30 a.m., with both her tormentors asleep, Alex Cooper crept out the kitchen door and ran barefoot through the frigid pre-dawn darkness, desperately seeking refuge in a town where everyone supported her captors. She couldn’t go home, because it was her Mormon parents who had forced her into this “conversion therapy” program to scare the gayness out of her.

The full title of Cooper’s memoir sounds sensational: Saving Alex: When I Was Fifteen I Told My Mormon Parents I Was Gay, and That’s When My Nightmare Began. But Cooper, with co-author Joanna Brooks, has succeeded in telling her story with a measured restraint and a calm maturity that belie her now 21 years.

Cooper doesn’t shy away from the grim details of her eight months trapped with an uneducated Mormon couple, their five children and the other “troubled teens” at the home. She was isolated, beaten and forced to wear a backpack loaded with heavy rocks to represent the burden of her homosexuality. She was told, “God has no place for people like you in his plan.” She tried many times to escape. She attempted suicide.

The facts are sufficiently brutal; wisely, Cooper doesn’t exploit them for shock value. Instead, she makes a sound case for the senselessness and danger of conversion therapy, now banned in several states. (It’s still legal under federal law in Canada, although last year Ontario became the first province to ban it.) Nor does she blame her parents. She’s remarkably forgiving of their well-meaning efforts to save their child, who she admits had a wild streak.

Saving Alex begins as a rebellious coming-of-age story but turns into an escape tale, then a legal thriller as Cooper fights for the right to live under the law’s protection as an openly gay teenager. Saving Alex is sure to become a clarion call to LGBT teens everywhere. “I realized that what made me different also made me strong,” she writes. She shows that for parents, too, it gets better.