A disease called the Wicked has split the world in two: the Wicked and the True . The Wicked roam freely, unbothered by the buzzing droves of Singers, the ultraviolet mosquito-like insects that carry the disease. They don't want for much - only to maim and dismember you. But don't worry: they always ask politely first. The True live in contained, isolated communities. They're the lucky ones; they found safety before losing their humanity to the Wicked. And while the threat of the Wicked may not be eliminated, for the True, the threat has certainly been contained. Sixteen-year-olds Astrid and Natalie are two of the lucky True.

Astrid lives in the glass-encased community of Goldsport where people spend their days lounging on the lawn, socializing and enjoying the seemingly endless stockpiles of food and supplies. No one is at all interested that the lighthouse on Puffin Rock has reignited - except for Astrid, that is. Astrid is determined to find out what is on that island, and she's dragging her ex-boyfriend Hank along for the ride. Natalie's grandfather long ago turned wicked and locked in their lighthouse on Puffin Rock, has finally succeeded: He's fixed the light in the lighthouse. The last thing Natalie needs is for the people of Goldsport to discover her family, especially now that her father has abandoned Natalie and her very pregnant mother. But Natalie's plan to stop Grandpa goes horribly awry, leaving Natalie and her mom trapped in the lighthouse themselves, hiding from their grandfather, who would dearly love to slit their throats. He loves them very much. And when Natalie's mother goes into labor, things only go from bad to worse.

But Astrid and Hank never make it out of Goldsport. Natalie is forced to leave the safety of Puffin Rock to save her baby sister. And what Astrid and Hank discover within Goldsport's walls, and what Natalie discovers outside them, will leave them all questioning what it truly means to be wicked.