Dead of Summer by Jessa Maxwell

Orla O’Connor hasn’t been to the isolated New England enclave of Hadley Island since she graduated from high school a decade ago. As a teenager, her best friend Alice disappeared from its shores without a trace—but with plenty of rumors.

Now, Orla returns to her family’s beachfront home to clean it out before her parents sell it. The island and her best friend’s house next door, abandoned after her family left in grief, are stirring up memories she would like to avoid. Then there are the locals, always gossiping and watching Orla’s every move. Worst of all, David, Orla’s childhood crush and son of a wealthy Manhattan family, is back for the summer with his new, impossibly pretty girlfriend, Faith.

Faith suspects that David is going to propose but as soon as she settles into his family’s sprawling Hadley Island estate, she feels out of place. She anticipated a luxurious summer of fun and romance, but David is never around—lured into business conversations with his entrepreneur father from dawn to dusk. With nothing else to do, Faith begins to investigate the island’s dark past, curious about what really happened to Alice all those years ago.

Meanwhile, local Henry hasn’t left his house since the young girl went missing, in an attempt to let the accusations against him die down. Except they never have. For years, Henry has had an endless supply of time to pursue his only hobby, watching the island from his telescope and recording the activities of its inhabitants. But Orla’s return has shaken him and lately he’s been seeing strange things: shadowy figures walking on the beach in the middle of the night and a light on in the upstairs window of the long-abandoned house of the missing girl.

When there’s another disappearance on the island, all three find themselves pulled into an eerie and twisty mystery that will haunt them for the rest of their lives.