Lennon Grant and her best friends since kindergarten, Margot, Johnny, Dylan, and Riley, share a terrible secret: on their high school graduation night, they were involved in a fatal accident that changed all of their lives forever. They all vowed to keep it a secret as they went their separate ways, but now, one year later, as they reunite for the summer, they are haunted by their deed, as a serial killer targets them and people close to them in Wai Huna. Someone knows what they did last summer. To stop the killer, Lennon and her friends will have to dig up their own painful pasts and in the process unearth the sordid history that the town fought to keep buried.