Surfing charters are meant to be a trip to Paradise. With six male surfers stuck on a boat, there's bound to be some friction. When two of the surf crew are replaced at the last minute with girls – the heat is turned way up. 

Tense surf saga loses footing near finale.

It takes about 40 minutes – and that’s approximately half its running time – to get a grip on exactly the kind of film Caught Inside actually is. That is, it’s a thriller, a sort of Dead Calm crossed with Donkey Punch sans the blood, sex and gob-smacking delight in horror-violence. But the first half is like a travelogue soapie, where the characters are sketched in ever so carefully and the personal tensions delineated with the kind of detail that suggests depth and gravity. In other words, the film feels less like a thriller in these long early scenes, rather more like a drama, but with most of the drama left out.

The setting is the Maldive Islands but most of the action is on board a small motor cruiser skippered by Peter Phelps, who is given the thankless role of ironic foil – he’s the guy driving the boat but primacy in a movie like this is all about who is the scariest. Aside from embodying aging and impotent masculinity, Phelps provides some much needed exposition, which is a plus, since the film is so full of pregnant pauses, and young pretty things, it needs someone of his bluster to charge it once in a while.

His passengers are surfers looking for some heartache scenery and cool tube action and underneath their glib glamour lies a cross-section of archetypal feminine guile and fragile machismo. There’s sensible Alex (Leeanna Walsman), who is making a video of the trip with boyfriend Toobs (Simon Lyndon), who exudes surfer cool. Rob (Sam Lyndon) is handsome, confident and possesses a certain deferential charm; Archie or Gromit (Harry Cook) is the youngest of the charter; he likes porn and drinking and speaks out of turn. The oldest of the group is Bull (Ben Oxenbould) whose character seems to have stepped out, fully formed from a Kem Nunn novel; even before he goes nuts in the movie’s second half, he comes off as savage and cruel. Bull is an incarnation of a certain kind of surfer-brute, living an insulated life in a 'code’ that seem less about pride and honour and more about territory, ego and violence.

Director Adam Blaiklock doesn’t do much foreshadowing of the terrors to come, Polanski-style; instead his camera is stoic, observational. The only real hint of how the plot will develop is the look in the eye of Bull when Alex turns up with gal-pal Sam (Daisy Betts), whose model good looks seem to send a collective shiver of unease amongst the men. 'No girlfriends," complains Bull.

In the script, by Blaiklock, Joe Velikovsky, and Matt Tomaszewski, this is one of the film’s more nuanced, intriguing moments – it suggests that Bull has some self-knowledge. (A little untypical of movie psychos, no?) Is he anticipating his own dark impulses? Of course, it could be read as garden-variety genre sign posting, where we can neatly label the villain, in the tradition of thrillers that trade in sexual violence, as a misogynist. But I suspect that Blaiklock and co. had something more ambitious and, dare I say it, subtle in mind. Not to give too much away, but what’s interesting about Caught Inside is that it’s not one or two 'triggers’ that send Bull off the deep end – he finishes the movie holding the cast captive, Cape Fear-style – but it’s a mess of sexual jealousy, combined with an identity crisis and perhaps an innate psychotic nature.

Still, sex and its dangers and misunderstandings are central to the film’s conceit; Sam is nursing the mortifying fact that a home-porn video she made for her ex has hit the digital super-highway. For Bull, this is a cue that Sam could be 'easy’. To Rob, she’s vulnerable. But it isn’t just envy over Rob’s success with Sam that sets Rob off. When he beats up a surfer for cheating him out of a wave, Sam is derisive. It’s not just a challenge to his masculinity, but his sense of tribalism. Of course, the irony is that Bull seems so alone with his mores and personal morality.

Caught Inside is full of good stuff. Oxenbould ultimately delivers a nerve-rattling job as Bull, and the rest of the cast do okay in the under-appreciated actor’s challenge of looking frightened. But for all of its incidental pleasures – including some crystalline surf action and spectacular sunset and ocean vistas – it’s a film that feels a little hollow. That’s because the ending indulges in the kind of blood-thirsty cathartic climax that seems to have staggered in from a very different kind of genre film. On one level, it's pure visceral filmmaker, a necessary bloodletting, and yet, it feels a little phoney and not quite right. By movie’s end, the characters no longer feel real – they’re just figures, playing a movie game.