Fourteen-year-old Eden McCoy doesn't fit in. All she's good at is running, and she doesn't even dare join the track team.

Her priority is to stay in the shadows and avoid the Glossies - a ruthless clique of girls who use social media to punish and humiliate their targets, led by their queen Bea and her sidekick Mikki. But one day, Eden breaks her vow to stay unnoticed: she beats track star Mikki in a race. This bold move captures the attention of Bea, who decides Eden needs to either prove her loyalty and become one of the Glossies - or suffer the consequences.

And so The Testing begins... As Eden is challenged to play a cruel prank on another kid or have that same act inflicted on her, her will is pushed to the limit. The only thing keeping her afloat is an unexpected connection with a boy called Riley, a fellow runner who messages her online.

But how deep does The Testing run? And how long until Eden breaks?