Gracie was born into a secret community hidden within ordinary society: the Perpetuals.

Her family are abnormally long-lived, resilient and fast-healing. But, it turns out, Gracie is mortal... which means she's vulnerable.

When the truth emerges, her immortal boyfriend Arty dumps her. Even worse, while her invincible peers embrace pulse-pounding extreme sports, Gracie's parents prepare to wrap her in cotton wool. Permitted 'one last adventure', Gracie heads on an international trip with her friends - though her hard-to-read ex, Arty, ends up joining them.

And, as they reach New York, things take a dark turn... Arty is hiding a dangerous secret that threatens to expose the whole Perpetual community. Could Gracie, a mortal girl, be the key to saving them all?