An adventurous young couple, Cliff and Cydney are celebrating theirhoneymoonby hiking to a remote beach inHawaii. The couple comes across two hitchhikers, Cleo and Kale, and a group of frightened hikers discussing a double murder in Honolulu of another newlywed couple on the island, with the victims having their teeth pulled out, and they begin to question whether they should turn back.
Unsure whether to stay or flee, Cliff and Cydney join up with another couple, Nick, who claims to have a titanium plate in his head and be a former special forces operative, and his longtime girlfriend, Gina, a former butcher. Far from civilization or rescue, everyone begins to look like a threat and nobody knows whom to trust. Gina and Cydney swap personal stories, and Cydney tells Gina about Rocky, a former lover who murdered a neighbor's dog and displayed the corpse while the two were having sex and threatened to kill her if she ever told. Eventually the two couples spy a police helicopter arresting Cleo and Kale, and a search of Kale's bag reveals aDentyne Icebox full of human teeth. Gina and Cydney reveal that each thought that the others were the killers, and the group continues to the beach.
After Cliff and Nick go kayaking to a nearby cove, Gina begins going through the other couple's wedding video, she inserts a memory card with a separate set of photos on and finds a shot that reveals that Cliff and Cydney are impostors. A series of flashbacks reveal that Cliff and Cydney are the killers, and have been killing people and then stealing their identities by ingratiating themselves with other couples while on vacation to learn their personal histories, mannerisms, and speech patterns. They killed the newlyweds from the wedding video and changed their appearances to look like them. We learn Cliff, revealed to be Rocky from Cydney's story, has been killing newlywed couples ever since he murdered the dog. Cydney, who was forced and eventually enjoyed participating in the murders, and Cliff learned more about their victims from all their friends and family talking about them in the wedding video. Earlier, Cliff planted the teeth in Cleo’s bag to frame both her and Kale.
Gina winds up on the top of the cave and sees Nick & Cliff below. Cliff shoots Nick in the back of the head, causing him to capsize. Cliff shoots at Gina but misses. Cydney fights Gina, but Cydney is thrown down and lands in the water. Gina runs and tries to call for help, but fails, and is nearly caught by Rocky before stabbing him through the hand with Cydney's knife. Gina runs, encountering another group of hikers looking for the stolen kayaks. Rocky attempts to convince the group that Gina is a crystal meth addict, and is having a delusional episode. His act seems convincing until one of the hikers, anEMT, points out that Rocky, not Gina, appears stoned, and Rocky shoots the entire group.
Meanwhile, Nick, having been saved by his titanium skull plate and hiding in the air pocket under the kayak, wakes up in the cave and goes to save Gina. Nick attacks Rocky, splitting his hand in half with a hatchet. Meanwhile, Cydney flags down a police helicopter. After nearly killing Rocky with the killer's .45 pistol, Gina jumps in the way of a police sniper and convinces Nick to drop the weapon, and the two embrace. Cydney sees Nick and Gina together and decides she will not go to prison for Rocky. She realizes how much she has changed for the worse, calling him, "The guy that fucked up my life." Cyndey informs the cops that the real killer is Cliff, and points out that he’s going for the gun while Nick and Gina have their backs to him. A sniper sees this and shoots Cliff in the forehead, killing him. It is unknown whether Cydney herself was arrested.
Gina and Nick are in the helicopter, and Nick proposes to Gina. After accepting, both suggest in unison to have no honeymoon.