Duke takes Audrey out to the island Carpenter's Knot on a motorboat. She asks why he requested she come with him and he answers that it's a surprise. He says that Vaughn Carpenter has given them permission to stay in his hotel, which is closed and has no other guests. They arrive and Audrey finds that Dave, Vince, Eleanor, Nathan, the Chief, and Eleanor's daughter Julia are there with a surprise birthday party.
Eleanor explains that Julia has been training in Doctors Without Borders for a while, which is why she hasn't been in town for a while. Nathan carts in several presents and says that he's starting to get over Jess. Vaughn greets them and says that his wife Olivia has recently died. When he sees Audrey, he's shocked and says she's the spitting image of his old friend, Lucy Ripley. Eager to learn more about the woman who could be her mother, Audrey tries to ask him about her, but the power goes out and he leaves to check on the generator.
Vaughn meets with the very much alive Olivia. He says he's getting weaker and the time has come for them to part. She tells him to be careful and leaves the hotel without the others seeing her. She leaves the island. Vaughn leans against a wall and his face distorts.
Eleanor suggests that they start the party, but Julia objects and says they should pick out their rooms first. Everybody goes to pick out their rooms. Nathan and his father are very uncomfortable around each other and separate. Audrey is more intent on finding out about Lucy. Duke says he will give his present last.
Vaughn steals Nathan's gun from his bag.
They decide to start the party, and Audrey walks in wearing a cute dress. She explains that she opened Vince's present early. Julia screams. They rush to her location, where she's found a molted skin in Vaughn's shape. The Chief takes charge. He explains that Vaughn was a Chameleon, a type of Troubled person he encountered back in 1983. It operates by draining a person of their life-force and memories, which kills them, shedding its skin, then shape-shifting into that person.
The Chief continues and says that back in 1983, the previous Chameleon killed several people this way, including his partner, before he was finally able to kill it. He warns that since "Vaughn" has already shed his skin, the Chameleon has already killed and replaced one of them. Everyone starts panicking and pointing fingers until Audrey exasperatedly orders them to calm down and use their heads. They find that the phone lines are down and they can't get a cellphone signal. Duke suggests they leave the island, but the Chief roars that they cannot let the Chameleon reach the mainland.
Julia accuses Audrey of being the Chameleon. Audrey tries to prove she's her by giving personal information, but Nathan points out that none of them know much about her, so they can't tell if she's telling the truth. As a show of good faith, Audrey hands over her gun. Duke asks Nathan and his father to hand over their guns, but Nathan says his gun is in his bag and the Chief says that he didn't bring one.
Nathan, Audrey, and the Chief search the boathouse, but when they find a boat, the Chief draws a hidden gun and shoots it full of holes. He says that he wasn't kidding when he said he wouldn't let the Chameleon reach the mainland.
Vince, Dave, Eleanor, and Julia start to get paranoid, especially when they catch Julia trying to pocket a knife.
The others come back inside and the Chief lies and says that they didn't find a boat. Duke found a radio and is trying to repair it. Nathan suggests finding the victim's body so they can find out who the Chameleon is. Duke stays with the radio while the others search the hotel.
Audrey tells the Chief she wishes he would talk to his son more often, but he reminds her that he's trying to toughen Nathan up.
Julia admits that she's terrified and Nathan calms her down. Everybody regroups and and finds several newspaper articles, including one of Audrey. There is one from 1983 about how Vaughn Carpenter was dying from meningitis but made a "miraculous" recovery. They figure the Chameleon took Vaughn's place 27 years ago, and Olivia played along so she'd have a perfect copy of her dead husband. Audrey talks to Dave, who wrote the article, and he insists that he didn't know that Vaughn had been replaced.
Duke walks in, carrying an axe, and explains that he searched the boathouse and saw the destroyed boat. He accuses Nathan of doing it, since he searched Nathan's bag and didn't find a gun. Audrey gets an idea and asks everyone to identify the presents they gave her before she opens them. They agree. Vince says it was the dress Audrey is wearing. Eleanor and Dave get theirs right. Nathan says his was a sweater, but Audrey opens it and it is a scarf. Duke attacks Nathan and the Chief knocks Nathan out with the butt of his gun.
The group ties Nathan up. Duke calls the Chief out on lying about whether or not he had a gun. Audrey calms them down and gets them to put down both of their weapons. Nathan wakes up and says that he asked Jess to buy and gift wrap the present a while ago, and she apparently bought the scarf instead of a sweater like he asked. The group starts arguing, but Audrey orders them to calm down and unties Nathan. The lights go out, and in the confusion, the Chief's gun is gone.
The group splits up and searches the hotel again. They hear a scream and find that Eleanor has fallen down the stairs and is dead. Duke finds the generator and gets it working again. Vince calls them into the main room, where a large crack has appeared in the wall. Nathan suddenly realizes something. He calls Audrey over and holds her hand. Grim with determination, he kisses her on the lips. She pulls away and asks what he thinks he's doing, but he draws the Chief's gun and shoots her. Everyone is shocked, but Nathan says that Audrey was the Chameleon. "Audrey's" skin starts to bubble and distort as the dying Chameleon asks how Nathan figured it out. Incredibly upset, Nathan whispers that he can feel Audrey, but he couldn't feel the Chameleon. The Chameleon apologizes and insists it didn't mean to hurt anyone. It lived peacefully as Vaughn for 27 years until the Troubles returned and it became hungry again. Eleanor fell down the stairs after being startled. It thought Audrey could help it, and explains that unlike its previous victims, the life-force drain didn't kill her. It then dies.
The group searches the hotel until they find Audrey unconscious in a trunk. Julia wakes her up and Nathan cries in relief.
Later, after they get back to Haven, Audrey explains that the Chameleon approached her and begged her to help it, but when she couldn't think of a way to do that, it drained her energy and knocked her out. When she wonders how close the creature duplicated her, Nathan admits it was close, but doesn't say he figured it out by kissing her duplicate. Julia is in shock over losing her mother and Duke says he will do his best to help her. The Chief complements his son on not hesitating when he shot the fake Audrey, but Nathan is disgusted and says he will never be like him.
The Teagues tell Julia to call them if she needs help. As they go, Vince notices a crack opening up in the cement, but walks away.
Duke finally gives Audrey his present, a necklace that says L.R. He explains that he, at age eight, was the boy standing near Lucy Ripley in the Colorado Kid photo.