Ever since, the nine survivors - just teenagers at the time - have met on the anniversary to remember those they lost. They made a promise to keep each other safe from harm. For Cassidy, always the outsider at school, this group has felt almost like friendship.
But this year, their reunion is overshadowed by death and the disappearance of one of their own. As the week unravels, Cassidy begins to fear something darker than survivors' guilt has bound them together. Was their pact to protect one another a promise, or a threat?