Nightfall - Jake Halpern

After fourteen years of Day, comes fourteen years of Night. Don't get left behind.
On Marin's island, sunrise doesn't come every twenty-four hours - it comes every twenty-eight years. Now the sun is just a sliver of light on the horizon. The weather is turning cold. The shadows are growing long. The dark is rising. And soon it will be Night.
The eerie Evening sunset is causing the tide to begin its slow roll out hundreds of miles, and so Marin, along with her twin brother Kana and the rest of the islanders, must frantically begin preparations to sail south, where they will wait out the long Night.
But first the house must be made ready for their departure. Locks must be taken off doors. Furniture must be arranged just so. Tables must be set as if for dinner. The rituals are bizarre - unnerving, even - but none of the adults will discuss why things must be this way. And then just as the ships are about to sail, the twins' friend Line goes missing. Marin and Kana know where he has gone, and that the only way to rescue him is to do it themselves. And surely the ships will wait? Because Night is falling. Their island is changing. And something is stirring in the dark.