Ever since Darby rescued her wild filly mustang, she's been having a tough time at her grandfather's ranch. And after she accidentally endangers one of his loyal and steady horses, she can't help but wonder if she really belongs on a horse ranch at all.

But then a shadowy horse shows up, prowling the grounds at night. Could it be the legendary Shining Stallion of Hawaii? And why is Darby the only one who has seen him? One thing is certain: When the mysterious stallion sets out to challenge the wrong horse, only Darby can stop him — before anyone gets hurt.