Seventeen-year-old Ollie fights to survive a deadly summer on an island off the coast of Maine after it is placed under quarantine due to a supernatural plague rising from the sea.

Two days before... Ollie Veltman is finally coming home to the quaint island of Anchor's Mercy after a year away while his mom battled cancer. It should be a celebration -- his mom is cancer free, and she's determined to have the best summer ever -- but Ollie's (now ex) best friends think he abandoned them, and he's returning with a lot questions. Because for a place that's perfect on the outside, a secret rots inside. A secret that could explain his mom's illness, and the illness of so many other locals. Ollie's desperate search for the truth turns life or death when a storm descends upon the island. In its wake, a long-sunken horror rises . . . Three weeks after... Ollie is being held in isolation aboard a military hospital ship in the harbor. They say he's a survivor, but they only know half the story. The truth is more dangerous than Ollie ever believed, and he suspects his saviors aren't here to save anyone. Only Ollie can stop what comes next, but that means getting back to Anchor's Mercy before it vanishes below the waves, taking with it everyone he has ever loved.