Scruffy and twisty, this honeymoon-from-hell thriller kind of unravels as it goes along. But before it succumbs to the formula, the actors manage to catch our attention, so we have to see it through to what'll surely be an outrageous finale.Cliff and Cydney (Zahn and Jovovich) are honeymooning in Kauai, where they decide to go on a two-day hike to an idyllic isolated beach, leaving just before hearing the news that there's a murderous couple on the loose. Soon they meet, and ditch, the rather shifty hitchhikers Cleo and Kale (Shelton and Hemsworth), then they decide to join another couple, Nick and Gina (Olyphant and Sanchez) for the hike. But Cleo and Kale catch up with them. And strange things start going snap in the jungle.From the beginning, we know writer-director Twohy intends on taking us for a ride, because of his purringly seductive filmmaking style and red herrings galore. Everyone looks suspicious, they all have secrets, and we quickly realise we can't trust anyone. Then Twohy starts layering in flashbacks to fill in the back-stories, up to an extended black and white sequence that sorts out the loose ends and sets things up for the frantic, action-charged climax.The first half of the film builds the atmosphere perfectly, establishing the characters with economy thanks to a clever script and an especially strong cast. Zahn and Jovovich are play against type effectively, and are terrific as the hapless lovebirds, while Olyplant and Sanchez are superb as their edgy new buddies. So by the time things start going nuts, everyone can generate jolts and humour at exactly the right moments.And boy do things get nuts. Not in any inventively unhinged way, but in the standard movie style of building to impossibly big action set pieces and then twisting them slightly, pausing for half a breath and then carrying on full speed. The gruesome, frenetic last act is utterly over-the-top, but still manages to be entertaining simply because it's so preposterous, and because we've come to like being around these characters who are now in a battle for their lives. And by the end, we've completely forgotten to care about all the gaping plot holes.