Two Can Keep a Secret is narrated in alternating chapters by Ellery and Malcolm, two high school seniors. Ellery and her twin brother Ezra arrive in Echo Ridge to live with their grandmother after their mother, Sadie, gets sent to court-appointed rehab. Neither Ellery or Ezra have ever been to their mother’s hometown, because she left shortly after her twin sister, Sadie, disappeared during senior prom, and she never came back, except to attend the funeral of her father, and her neighbor’s daughter, Lacey, who was murdered five years ago at the amusement park outside of town.