Mara might look like your typical teenage girl that attends high school, but she is not anymore. Mara was involved a a horrible accident that left her as the only survivor and her friends all died. Mara with her family relocate to Miami, FL. She has to begin school in the middle of the term while dealing with her post traumatic stress disorder (PTSD). Then, she meets Noah, and falls in love. Their relationship then becomes a main focus of the story.
With the first person point of view, it's hard to tell if everything the narrator says if reliable. Thus, the ending doesn't seem to make a lot of sense. The flashbacks add to the eeriness of the book but also makes the story very unclear.
If you are confused about the ending, don't worry, I think most people are, we must wait for the sequel to come out, I guess...