Duke takes Audrey out on a boat at 8 a.m. on a Saturday, and she asks why he's taking her out to the nearby island of Carpenter's Knot. He insists that he wants to show her the spot where he meditates. As they approach the island, Duke explains that Vaughn Carpenter, the last surviving member of the Carpenter clan, lives there and closed the family hotel there years ago when Duke was a kid. When they arrive, Duke takes Audrey up to the hotel and she discovers that Eleanor, the Teagues, Nathan, his father, and Eleanor's daughter Julia are there to throw her a surprise party.
Eleanor introduces her daughter and explains that she is in town but has been gone with Doctors Without Borders for years. Nathan arrives with a cart of presents and admits he's trying to get over Jess. Vaughn arrives and greets them, and then claims that his wife Olivia is dead. When they introduce him to Audrey, he says that she looks just like Lucy Ripley, an old friend. The power goes out and Vaughn leaves to check on it before Audrey can answer him any other questions.
Upstairs, Vaughn tells Olivia that he's getting weaker and sends her on her way. She tells him to be careful and leaves without the others seeing her. Once she's gone, Vaughn leans against the wall and his face distorts.
Eleanor takes command and tells them to start the party, but Julia objects and says they should pick out their rooms first. They all go off to find rooms, and the Chief awkwardly offers to help Nathan. Nathan refuses and says he's going for a walk. Once they're alone, Duke admits that he's not much for gift-giving, and Audrey says she wants to go find Lucy first. Disappointed, Duke says he'll give her the gift later.
Vaughn goes to Nathan's room and takes his gun out of his duffle bag.
Later, everyone gathers and waits for Audrey, and Eleanor sends Julia and Nathan to find Audrey. She arrives before they can go looking, wearing Vince's dress as an early present. Julia goes out and they hear her scream, and they go to investigate. She's found a molted skin in the shape of Vaughn. Chief Wournos recognizes it and explains that Vaughn was a chameleon, a monstrous shapeshifter. He warns that it's shed its skin and taken the form of one of them... and killed the original.
Back in the main room, Chief Wournos explains that he saw one of the chameleons when he came back from Vietnam and had to kill the creature when it took on the form of his partner. He explains that they have to stay together because the shapeshifting process takes time to mimic its victim's soul. Chief Wournos figures that the chameleon is becoming active because the Troubles are coming back, and that it won't stop at one victim. Duke wonders how it happened to show up at the party and the Teagues admit that "Vaughn" invited them, and then Eleanor proposed the party and they decided to use the hotel. They start arguing until Audrey breaks it up, and they realize the land lines are down and they can't get a cell phone signal. Duke suggests they look for a dinghy at the boathouse, but Chief Wournos refuses to let them give the creature a chance to get to the mainland.
Audrey suggests that they check the boathouse before making any decisions, and Julia points out that she's the only one who has the gun. Audrey insists she's who she appears to be and gives them personal information, but Nathan points out they don't know enough about her to know if she's telling the truth. In response, Audrey gives over her regular gun and her hidden gun. Duke insists that Nathan and the Chief hand over their weapons. Nathan says his gun is upstairs in his bag, and the Chief says he didn't bring a gun to a party.
As it continues to storm, Nathan, Audrey, and Chief Wournos go to the boathouse. Nathan and Audrey go inside and find the dinghy, and Audrey thanks Nathan for backing him up. As they work, he thanks Audrey for asking about Jess. Chief Wournos comes in as they find the inflatable dinghy.
At the hotel, Dave and Vince wonder which one of them is the chameleon and start to suspect each other. Julia pockets a cheese knife but Eleanor spots her. She admits she doesn't understand Julia at all, and then apologizes and says she doesn't want to fight.
At the boathouse, Chief Wournos takes out his gun and shoots the boat, and explains that he won't let the chameleon escape. Either they kill it or it kills them. They return to the hotel and the Chief lies about finding a boat. Duke has gone alone to the attic and come back with a radio, and he works to fix it. Nathan suggests that they find the victim so they can identify who the chameleon is. Audrey goes with the Chief to search while the Teagues go on their own and Nathan accompanies the Carrs.
As Audrey and Chief Wournos search, Audrey notes that Nathan is in a dark place, but the Chief insists he shouldn't talk to his son. Audrey finds a panel concealing a dumbwaiter and he compliments her, and she suggests he compliment his son. Chief Wournos insists that he has to be hard on Nathan so he can handle things after he's gone.
Nathan approaches Julia, who is scared and angry at her mother. Nathan and Audrey arrive and they continue searching, and Julia goes with Nathan and Audrey. She admits that she hoped to learn enough out in the world to deal with her mother, but regrets coming back. As they talk, Julia finds newspaper clipping, including one of Audrey. Other clippings show how Vaughn died of bacterial meningitis but then 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. Dave insists that "Vaughn" is afflicted like the others, and that Lucy helped the Troubled. Because of that, the chameleon was interested in Audrey.
Duke comes back from the boathouse with an axe and tells the others that the boat is destroyed. He accuses Nathan of shooting it and says that he searched Nathan's bag and there's no sign of the gun. Audrey calms them down and gets an idea. She goes to the presents and explains that each person will tell what they gave her before they open the present. The chameleon won't know what everyone got Audrey. The others agree, but Duke insists on going first. Dave identifies the dress he gave Audrey. Eleanor and Dave identify their gifts, but Nathan is wrong when he says it's a sweater, but it's really a scarf. Nathan and Duke fight and Chief Wournos knocks "Nathan" out using the butt of his gun.
The group ties Nathan up and Duke points out that the Chief has a gun. He reluctantly gives up his gun, and Duke removes the head from the axe. Nathan wakes up and explains that he asked Jess to get the sweater but she picked a scarf instead. They start fighting again until Audrey calms them down and unties Nathan. The lights go out and everyone scatters, and Duke discovers that someone took the gun. Nathan figures the chameleon is deliberately scattering them so it can pick them off one at a time.
Eleanor and Chief Wournos find this, and the Chief vows to find and kill it. Meanwhile, Julia hides beneath a bed as someone searches nearby. Audrey, Nathan, and Duke discover that the fuse box has been sabotaged and split up to search. They hear a scream and run to the stairs, and find Eleanor dead of a broken neck. Chief Wournos is standing over her and admits that she's gone. Duke gets the generator running and they figure that Eleanor died of an accident. Vince calls them into the main room, where a large crack has appeared in the wall. Nathan notices the ropes from when Audrey untied him earlier, and asks Audrey to come over. He takes her hand and then kisses her. When everyone wonders what he's doing, Nathan takes his gun and shoots him. He explains that he can feel Audrey's touch, but couldn't feel the chameleon's. The chameleon apologizes and insists it didn't mean to hurt anyone. Eleanor died when, startled, she felt down the stairs. The chameleon thought that Audrey could help it, and explains that the agent should have died but didn't.
The chameleon directs them to a storage room where they find Audrey, unconscious, in a trunk. Julia wakes her up and Nathan cries in relief.
Later on the mainland, Audrey explains that the chameleon came to her for help, and she didn't know how. 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. Duke tells them that Julia is in shock. As Nathan leaves and Chief Wournos admits he's proud of him for shooting his partner. Nathan has no interest in being like his father and walks away.
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 approaches Audrey and gives her his present: a necklace with the initials LR. He explains that he was the boy in the Colorado Kid photo with Audrey's mother.