12-year-old Lark Heron-Finch is steeling herself to spend the summer on Swallowtail Island off the shores of Lake Erie. It's the first time she and her sister will have seen the old house since their mom passed away. The island's always been full of happy memories--and with a step father and his boys and no mom, now everything is different. When Nadine, a close family friend, tells Lark about a tragic boat accident that happened off the coast many years before, Lark's enthralled with the story. Nadine's working on a book about Dinah Purdy, Swallowtail's oldest resident who had a connection to the crash, and she's sure that the accident was not as it appeared. And then Lark discovers something amazing. Something linked to the crash and to her own family's history with Swallowtail. But there are others on the island who would do anything to keep the truth buried in the watery depths of the past...