When the truth comes out of the shadows, it can spark an unforgettable adventure. In the world of Greycloak Island, the souls of disobedient children can "break" and release dangerous shadow creatures. To protect everyone, good behaviour is strictly enforced. Young Myrtle Rainwater is very well-behaved. At least, she thinks she is. But when she finds a panther soulshadow wearing the name tag "Six" in the bathroom of her grim boarding school, she comes to realize that - impossibly - he is hers. Horrified and ashamed, Myrtle makes the fateful decision to hide him and flee the school with her mischievous sister, Natty. But the ensuing adventure leads Myrtle to question everything she's been told.

What are soulshadows, really? What happens to these creatures and their children after they are captured by the authorities? And why does the Grand Principal, the mysterious leader of the government, seem have a special interest in Myrtle's fate? When the answers to Myrtle's unsettling questions are revealed, can Myrtle keep her heart - and soul - from breaking apart forever?.