Henry Dunn returns home to Harper's Island, where seven brutal murders were committed seven years ago, with his bride Trish, daughter of tycoon Thomas Wellington, and a large wedding party, stirring memories and emotions before and after arrival. Henry's popular uncle Marty overhears Thomas plot with Trish's irresistibly sexy ex Hunter Jennings to seduce her away, but is brutally murdered while returning trough the woods.

The bride & groom host a scavenger hunt for their friends, most of whom wind up socializing with the locals instead. Trish's old flame turns up unexpectedly; Henry's brother can't stay out of trouble.

Henry goes skeet shooting with his future in-laws, while Trish's bridesmaids help her try to get rid of Hunter before Henry finds out. Sully steps up his flirtations with Chloe, but she only has eyes for Cal. Sheriff Mills investigates Kelly's apparent suicide, which causes even more tension between Shane and JD. After Henry confronts Tom over his meddling, Tom pays off Hunter to leave the island.

For his bachelor party Henry's friends take him fishing where they find more than fish. Katherine hires a psychic for the start of Trish's bachelorette party but the psychic reacts badly to Abby. Malcolm pitches his business plan to Thomas and Richard but it fails to attract interest.

Feeling stressed about the wedding Henry encourages Trish and Thomas to take some time out but they encounter a trip wire which knocks them from their bicycles and then they are set upon by an Alsatian. Malcolm is feeling very stressed over Booth's death and makes up excuses to the other guys about his sudden disappearance. Sheriff Mills finds the dismembered body of Reverend Fine in the lake and Abby finds out that her dad is conducting an investigation into mysterious deaths that have happened on Harper's Island since Wakefield was killed.

After the killing of Thomas Wellington the entire wedding party are spooked and are questioned in detail by Sheriff Mills. J.D. and Abby find the mutilated body of Marty Dunn and leads to Abby showing J.D. & Henry's her father's murder board. Believing that John Wakefield didn't die 7 years previously and is responsible for the recent deaths Abby and Henry dig up the grave of John Wakefield but they find his skeleton in the casket. Another wedding guest meets a grizzly end. Meanwhile, Cal and Chloe go to great lengths to get back the engagement ring that Cal lost.

In the wake of more deaths, the wedding party pack their bags to return to Seattle. When the sheriff investigates at the Candlewick, Malcolm feels a sudden need to repack his luggage. Henry tries to comfort Trish, but she rebuffs him after learning that JD is the prime suspect. Abby spends time with Trish, comforting her and reminding her of her love for Henry. A disfigured stranger's identity is revealed. Abby recollects several incidents on the island before the Wakefield murders and learns something she never knew about her mother. Madison is lured away from the ...

Evacuation plans are put on hold when Madison turns up missing. In searching the island for her, the friends discover more bodies. Trish smooths over her tense relationship with Henry while his brother stews in jail, but a strange invasion there allows JD to escape. Sheriff Mills is seriously injured while trekking through the woods and is cared for by an old acquaintance, but the help is short lived when a fire breaks out. Abby receives a phone call from the kidnapped Madison, who says she'll be killed if any of them try to flee the island. Sully wants to leave ...

While the survivors gather at the Candlewick, Chloe and Abby help Cal to patch up the sheriff. Shane turns up to taunt the group, but Henry arrives in time to stop him. Jimmy gives Henry some critical papers from JD's pocket which lead Abby to question her own paternity. When Beth disappears, the friends search a tunnel network beneath the inn. Henry and Jimmy need Shane's truck to rescue Abby, but the vehicle is swiped by Trish and Shea. The sheriff disappears from Cal's care; Madison's recovery throws new suspicion on someone close to Abby.

Madison's words ostracize Abby from the group, but they all determine to leave the island. Henry and Abby stop to pick up Cal and Chloe but are dismayed to learn that the sheriff is gone. When state troopers arrive for custody of JD, they get an unpleasant surprise. Trish is let in on the secret of the attic. An attack on the marina leaves Henry injured but spells worse for Jimmy. Henry tries to shield Abby from accusations as the group holes up in Cannery Row bar, where the killer mounts a fresh attack and leaves a surprise. Chloe exchanges a tender goodbye with Cal ...

Abby's mourning is cut short by shock, but friends prevent her from being lured away by revenge. Madison tells Shea about her new friend; Abby tells Henry and Danny that she is not Wakefield's child. Shane makes a stand during another attack on Cannery Row. Sully and Cal discover a new comradeship; while Abby, Henry, and Danny return to a gruesome scene at the bar. Friends rendezvous at the chapel, where Chloe is kidnapped; they make a plan to flush out the killer in the Candlewick tunnels. Cal risks everything to save the love of his life; Shea finds a terrifying ...

Sully and Danny flush out a killer; when Abby can't finish him off, he's dragged to jail instead. Feeling safer now, the friends split up. Sully tries his hand at interrogation as well as fixing a radio. Abby retrieves Shea and Madison; Henry goes to fetch Trish, but she has been lured out to the bluffs by Jimmy with talk of a rescue boat. Abby confronts one killer, but Madison soon reveals that her kidnapper had a "friend." Shea shares her discovery with the others; when Jimmy reports back that Trish accidentally slipped down the rocks, suspicion immediately falls on...

Two people escape the island even as more victims pile up. A final standoff in the church leads to a fire and a killer's revelation. Abby is held captive and must fight to save herself; survivors are questioned by police.