We flashback to Harper's Island sixteen years earlier and find a young Abby and Henry playing on the floor of Abby's home. The summer has come to an end. As Henry's parents arrive to take him back to the mainland, Henry and Abby run down to the beach. Abby whispers something in Henry’s ear and as he looks into Abby's eyes, Henry tells her goodbye. Present day, Henry tells Wakefield that killing Trish was harder than the others, while Wakefield says that Danny's fight and death wasn't an embarrassment. Henry reminds him that they only have a couple hours before the Coast Guard arrives so they must move on. Shea and Madison make it to the boat house and tell Sully about Wakefield's escape and Danny's death. Sully takes a boat hanging from the rafters and puts Shea and Madison on it, out to sea while he stays behind. Henry links up with Sully at the boat house where they get the news that the Coast Guard will arrive in 45 minutes and everyone is to meet them at the Marina. The two of them head out to find Trish. Henry confesses to Sully about all the people he's killed. At first, Sully thinks that Henry is joking but as he realizes that Henry is serious, Sully attempts to shoot Henry but fails. Because at the boat house, Henry removed the bullets from Sully's shotgun. With Wakefield watching, Henry then kills Sully. Wakefield tells Henry that it's time to finish it, it's time to kill Abby. Henry finds Abby and Jimmy and they break the news to him that Trish is dead. Henry plays along and follows them to where they found her body, but now it's gone. Henry tells them he doesn't believe she's dead and takes off, leading them to the church where they find Trish's body, laid out on altar. As they approach the altar, Wakefield surprises them from behind and attacks Jimmy. Jimmy tells Abby to run and she escapes and heads toward the marina. Jimmy is able to fend Wakefield off by shoving a flare into his midsection. In doing so, sparks flare and the curtains catch on fire. Wakefield blows their cover as he tells Henry that Abby is getting away. As Jimmy tries to leave the church, Henry shoots him in the back. Having incapacitated Jimmy, Henry goes after Abby. He finds her and tells her that Jimmy is dead. Together they head toward the marina. As they run, Abby begins to piece together that Henry's story isn't adding up. When Abby calls him on his lie, Henry creeps toward Abby, switch blade in hand. Unaware that Wakefield has approached her from behind, Abby steps away from Henry. Instead of killing Abby, Henry stabs Wakefield in the chest. Before he dies, Wakefield's last word is, "Henry." It's now clear to Abby that Henry was Wakefield's accomplice, but before she can get away, Henry throws her to the ground, knocking her out. Back on the Mainland a few days later, Shea and Madison speak with the FBI. The FBI tells them that they are the only survivors on the island and those that were still alive before they left were found dead, most perishing in the church fire. Meanwhile on Harper's Island, Abby awakens in a strange house. At the bottom of the stairs, Henry greets herand tells her the truth - he chose her over his father, John Wakefield. Wakefield wanted Henry to kill Abby but because he loved her, he couldn't. Abby tries to escape but all the doors are locked, so she retreats to the room she awoke in. On the other side of her door, Henry reminisces about their childhood and reminds her of what Abby told him on the beach sixteen years earlier, "I wish you could live here with me forever, just the two us." He says that they can now, just the two of them. Abby slumps down on the floor against the door, taking this all in. Henry checks on Abby later, but finds Abby armed with a large piece of glass she's pointing at him. She wants to know how he could have done all this and Henry then explains how he came to know Wakefield and the events that led him to this. Abby breaks through a glass door with a telescope and runs into the garage where she finds Jimmy alive and bound inside. Henry explains his plan: Jimmy will sign a confession, taking the blame as Wakefield's accomplice since Shea and Madison made it off the island. Back in her room, Abby tries to find a way out. She spies the wall hook. When Henry takes Abby back to see Jimmy one last time before he kills him, Abby goes to Jimmy and kisses him putting the wall hook into his mouth. When she tells Henry that she loves Jimmy, Henry pulls her away, slaps her and Abby falls to the ground. Spying a screw driver on the floor near her, Abby stabs Henry in the foot and flees the garage. Henry runs after her brandishing a boarding knife. As she reaches the cliff, Henry tells her he could never hurt her, she's all he wants and to prove it, he throws the knife over the cliff. At that moment, Jimmy enters the frame, tackling Henry and together they fall off the cliff. Abby runs down to the beach and finds Jimmy. As she goes to him, Henry approaches her and she stabs him with the boarding knife. As he dies, his last words to Abby are, "I love you." Jimmy and Abby are rescued. As their boat takes them away from the island, they are at last, safe in each other's arms.