One year ago Hannah's older brother Tom died in a motorbike accident.

On the anniversary of his death, she returns to the bridge where it happened and finds two teenagers waiting for her; Cam, who doesn't talk, and Rylie, who seems to resent the fact that Hannah has seen them at all.

Dared into joining their Run, Hannah quickly realises her night has gone seriously weird.

How are they able to Run for so long – and so far – without feeling tired?

Who are the children that Rylie is Tracking – and how is she doing it?

How does Cam unlock doors with just a touch?

And why can't anyone see them?

But it isn't until Cam is forced to unveil his own strange, unsettling powers that Hannah finally starts to understand – and has to face her own past...