As the final surviving members of the wedding party battle to get off the island, the truth is finally revealed.

As the killer's murderous rampage continues, the group starts fighting back when they discover a possible way off the island. However, happiness quickly turns to horror when the possibility of an accomplice sows mistrust among the surviving guests.

The group narrowly escapes The Cannery and are drawn to the church when the bells start ringing, thinking it's a sign from one of their group. However, when another person disappears, they are forced to split up to simultaneously block off the exits to the underground tunnels and search for their missing friend.

Madison reveals who is responsible for her disappearance, leaving the remaining guests stunned and confused. When an attempt to flee the island in Jimmy's boat results in disaster, the group are forced to take refuge at The Cannery.

Tensions rise after John Wakefield's journal is discovered, and the guests who are still trapped in the Candlewick Inn begin to turn on one another. However, when they uncover a labyrinth of old tunnels beneath the hotel, they are forced to come together to find missing guests. Isolated from the main group, Cal and Chloe attempt to deal with the Sheriff's injuries but find themselves distracted.

As people prepare to evacuate the island, one wedding guest mysteriously disappears. Several of the wedding party reluctantly volunteer to stay behind and search the island, but the situation changes when Abby receives a distressing phone call. Sheriff Mills continues his search for the killer, but finds himself in a dangerous game of cat and mouse.

The atmosphere at the Candlewick Inn darkens when the Sheriff begins conducting searches of everyone's rooms, suspecting one of the wedding party is the killer. New information reveals an eerie connection between Abby and Wakefield, and the tragic events of seven years ago. Malcolm stresses over the possibility that police will find the bag of cash he's concealing and begins to unravel.

With the wedding party reeling after the events at the rehearsal, Abby, Henry, and J.D. decide to take the investigation into their own hands. Wellington family secrets are revealed when the Sheriff refuses to let anyone leave the island until he questions them.

Henry encourages Trish and Thomas to take a father/daughter bike ride in the woods to relive Trish's wedding stress. Abby tries to repair her relationship with her father, but ends up uncovering the Sheriff's secret. Danny and Sully begin to grow concerned about Joel. Trish and Henry's wedding rehearsal takes an unexpected turn.

When the groomsmen take Henry fishing for his bachelor party, the make a gruesome discovery. The bridesmaids celebrate Trish's final days as a bachelorette with a psychic tarot card reader hired by Shea. Abby and Jimmy consider rekindling their relationship.

When a local'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 her future.

The wedding party heads out on a scavenger hunt and the competition soon heats up. Against her better judgement, Trish secretly meets up with an old flame, Hunter Jennings. Abby re-connects with the island locals and runs into a friend who is still haunted by John Wakefield.

Abby Mills returns to Harper's Island to attend the wedding of her best friend, Henry Dunn, and his fiancée, Trish Wellington. Abby hasn't been home in seven years, since her mother and five others were brutally murdered by serial killer John Wakefield.