Cliff & Cydney (Zahn and Jovovich) are newlyweds who have come to Hawaii for their honeymoon. As they plan their vacation and hope to find a secluded beach beauty-spot, they learn that there has been a grisly murder on one of the other islands - and now it seems that the murderers have jumped over to join them. After a run-in with a highly-suspicious and angry couple, they meet Nick & Gina (Olyphant & Sanchez) who seem like your average, everyday team ... except overly-talkative ex-special forces soldier Nick has taken along a bow and arrow on his trip, and likes to kill his own food.

Chris Hemsworth and his angry girlfriend are picked up by the cops on the island. When they find a bag full of teeth in his rucksack, it's all the evidence they need and they are bundled onto a chopper and taken away. Young Thor doesn't look too happy.

Cliff & Cydney confide in their new friends that they thought the killers were Nick and Gina. It's all laughed off as they reach the secluded beach. They are also joined by a few frat boys on canoes.

Cliff suddenly perks up and borrows two canoes, and convinces Nick to join him to explore some of the caves. Nicks finally concedes and follows his new buddy. Gina finds Cydney's camera and starts to take a look ... but something sets off the alarm bells.

She races after Nick to try and get his attention, but it's too late and he's too far out. She panics and runs after them keeping to the shoreline. We see the still she was looking at - the happy couple at the wedding ... except they are not Cliff & Cydney. Cydney realises something is up when she finds the discarded camera, and gives chase.

Cliff leads Nick into a cave. After a little talk, he removes his glasses and goes a little psycho. He takes out a gun.

Flashback time. We see that Cliff and Cydney are the murderers. Then that Nick and Gina are normal human beings, and Gina desperately wants to get married. Nick returns to a ring store on the island and shows the cashier a ring he has already bought, and is pleased to hear it'll do the trick.  So now everything's good, and we're going to root for the previously psycho-Nick and his girl, over the newly psycho Cliff and his girl.

Gina makes it to the top of the cave and peers inside through a hole just in time to see Rocky/Cliff shoot Nick in the head. Gina screams. Rocky tries to shoot her too, but misses.

Cydney shows up and fights with poor Gina on the cliff-top, and stabs her in the leg. Gina shows Cydney the smackdown and her nemesis falls through the crack in the cave roof.

Gina hangs around and tries to phone for help. She instead gets a cold call from an Indian guy, and convinces him to call the cops for her.

Then she can hear a sound like a radio crackle. She walks to the cliff edge to see Cydney out at sea in a canoe ... and guiding Rocky to her position. Rocky tries to shoot her again but can just hit her in the hand. Gina retaliates and slams the knife from her leg into his hand and runs away.

But wait --- Nick is still alive. The bullet hit the metal plate in his head, and even though you might think it'll have torn his eyes from their sockets and given him quite a serious headache, he's none the worse for wear. He gets back into his canoe and back into the fight to rescue Gina.

Gina is running back to the beach when she runs into the frat boys looking for their canoes. Rocky catches up and tells them that she is just high on drugs. Some of them are med students and want to help. One doesn't believe Rocky when he looks into his eyes. So Rocky takes out his gun and this time, having had some practice, is a crack-shot and takes them all out.

Nick shows up just in time - and slices straight through Rock's hand in quite a nice action shot! But Nick has taken another bullet it seems.

Cydney gets to the beach first and waves down a chopper --- that Indian callworker must have been quite convincing!

Nick gets the better of Rocky and holds a knife to his throat when the chopper hovers overhead. Nick isn't ready to let him go. Cydney tells the chopper Sniper that the murderer is Nick.

Suddenly Gina jumps in the way and drags Nick away. Rocky isn't about to give up. Cydney can see this and has a change of heart - she tells the sniper that the man on the ground is the one that has stolen her life away from her. Rocky reaches for a gun as the sniper takes him out.

Later, Nick and Gina are airlifted away. He presents her with the ring and proposes. She accepts, but isn't happy that it took him a few years. They both decide that they don't need to plan anywhere for their honeymoon!

So, yeah, they cheated.  There's a whole IMDB forum about this with some angry dudes debating it, who are no doubt linked to the movie in some way because, well, surely there's more important things in life to get angry about.  So it goes like this  - Cliff & Cydney act like innocent honeymooners all the way through, fair enough, but then they start to suspect other people - and talk together in their tent, out of reach of Nick & Gina, and suspect them of the murders.  Clearly this was just for our benefit, so we're torn between thinking it's Nick & Gina, Thor & his girl, or somebody else - but definitely not our heroes.

Obviously, movies with a real, mind-blowing twist are hard to make (Usual Suspects, Sixth Sense etc etc), but to so blatantly throw us off the scent is just annoying and lazy.

BUT - on saying all this - there is one good thing from it.  The opening sequence in the jeep has the most clumsy, heavy-handed, backstory geared dialogue I've ever heard in a movie -- wait for it --

"Hey, can I ask you a question, Mr. Cliff Anderson ... from Venice Beach, California?"
"Yes, Mrs. Sydney Anderson, formerly Miss Sydney Carswell, of Pacific Palisades, California."

Argh!! Almost made me turn off after the first few minutes.  Just really terrible writing ... BUT (!) of course, the purpose of that (we're meant to believe) was as a practice-run of their new personas and as a test for each other.  Still, you had to wait until the end to appreciate that - and most would have forgotten by then, and still the real reason was just lazy writing to learn more about the two main characters in Miller time ... so it should have been handled better.