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 wedding party heads out on a scavenger hunt. While out, Trish meets up with an old flame, Henry talks to the locals, and Abby runs into a friend who has been haunted by John Wakefield.

When a local girl’s death is ruled a suicide, Abby challenges her father, the Sheriff, to investigate what really happened. As the wedding approaches, Trish must come to a decision about Hunter.

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.

A father/daughter bike ride in the woods leads to a startling revelation. Abby uncovers the Sheriff's secret obsession as Trish and Henry's wedding rehearsal takes an unexpected turn.

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The wedding guests begin preparing to leave the island but the Sheriff suspects that one of them is the killer. Some new information reveals an eerie connection between Abby and Wakefield.

As the guests get ready to leave the island, one guest mysteriously disappears. Abby receives a phone call from someone threatening to kill the missing guest if anyone leaves the island.

The group turn against each other. However they find a map and are forced to come together to find Madison.

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.

Abby confronts the killer, but the guests start thinking he may have an accomplice. Another guest dies and another goes missing.

Eight of the suspects battle for survival as the truth is revealed.

The answers are finally unveiled in the season finale.