Fifteen-year-old Itsuki Amazawa has come to visit the island for the very first time. At his adoptive mother's childhood home, he and his newly met cousins pass the summer days in peace and quiet.

That is, until Itsuki learns the truth about the island...

Strange incidents known to the locals as "Shikinejima Vanishings" have been occurring around the island. And deeply entangled in these puzzling happenings are people that Itsuki holds dear.

Will he be able to uncover the truth and save those he cares about?