Seven years after her mother and five others were murdered on Harper's Island, Abby Mills returns for the wedding of her best friend, but a week of celebration turns to a fight for survival as people start dying.

Trish confronts an old flame when the wedding party embarks on a scavenger hunt; Henry makes peace with some of the locals; Abby meets up with a friend who is haunted by John Wakefield and the island's tragic past.

A supposed suicide puts the wedding guests and the locals on edge; Trish must make a decision about Hunter.

A gruesome discovery disrupts the festivities when the groomsmen take Henry fishing for his bachelor party; the bridesmaids celebrate Trish's final days as a bachelorette with a psychic who reacts strongly to Abby.

A father-daughter bike ride in the woods leads to a shocking revelation; Abby learns about the sheriff's secret obsession; Trish and Henry's wedding rehearsal takes an unexpected turn.

After the deadly events at the wedding rehearsal, Abby, Henry and J.D. take matters into their own hands and try to solve the murder by themselves.