Without family, who will watch your back?

Megan suffers a major tragedy when her son and husband are killed in a car crash. After four years in a mental health institution, she goes to stay with her brother in her hometown, to attempt to get her life back together. But once Megan arrives, her brother disappears. And now none of the townspeople remember him ever existing! Is Megan losing her mind, or is there something more nefarious at work here?