Abby Mills returns to Harper's Island for the wedding celebration of her best friend, Henry Dunn, and his fiance, Trish Wellington. Abby hasn't been home in seven years, since her mother and five others were murdered by John Wakefield.
The groomsmen take Henry fishing for his bachelor party and make a gruesome discovery. The bridesmaids celebrate Trish's final days as a bachelorette with a psychic who has a very strong reaction to Abby.
An attempt to leave the island after Katherine has been killed turns into a disaster that will keep the remaining members of the wedding trapped for now. Meanwhile they find out a secret that will leave them reeling, and four more victims are claimed.