Drowning by numbers: "Night Swim"

It's not the worst idea on Blumhouse's part: offer the audience kebab and chips when the rest of the film world is competing for Michelin stars. This time last year, the tactic gave us the enjoyable killer-doll horror M3gan; this year, we have the killer-pool movie Night Swim, which the writer-director pair of Rod Blackhurst and Bryce McGuire have expanded from their 2014 short of the same name. Yes, you read that right: killer swimming pool movie, the kind of enticingly dumb-as-nuts premise you might have stumbled across in a video rental emporium circa 1982, now elevated to the third biggest screen at your local megaplex. But don't go fishing around for your verruca sock just yet. The advantage M3gan possessed was that its devil doll could (and did) go everywhere on two automated legs. By contrast, Blackhurst and McGuire have had to find more ways for oblivious or plain stoopid characters to come for a fateful dip in the back garden of the new house ailing baseball star Wyatt Russell and stock horror wife Kerry Condon have bought for their young family. The motivation feels vaguely organic when Russell's sluggish slugger starts out on a course of hydrotherapy. It feels a lot less so - feels comically contrived, indeed - when daughter Izzy (Amélie Hoeferle) is handed a flyer by a representative of the school's Christian swim meet, or dad invites the neighbours round for a life-threatening pool party. Whenever these characters aren't within an arm's length of the killer swimming pool - whenever they're at school or baseball practice or in hospital or visiting the house's previous owner - you can hear the executives urgently scribbling and passing the filmmakers notes: why are the characters not at or around the killer swimming pool?

You want to give Blackhurst and McGuire their dues for landing on an original-ish idea, but there may well be a reason no-one's thought to make this particular movie before, and that may well be because it's simply very hard to get it to work at ninety minutes. (This idea may just be inherently better suited to a short, or sounds better in pitch form; I spent much of the duration wondering whether this set-up would have generated altogether more persuasive action had it been a killer municipal pool, which would at least have had willing victims queuing up to take a dive.) There are flickers that Blackhurst and McGuire are onto something: it's sorta fun that the water should have the same regenerative effect on Russell as the blood of virgins reportedly had on Elizabeth Bathory. Yet the filmmakers seem determined to filter any campier traces of enjoyment out of their premise - Night Swim is the anti-M3gan, in this respect. It's an oddly sombre proposition, both for a Blumhouse movie and a killer swimming pool movie: shot in blues and greys and played deathly straight, swerving, say, any of the poolside heavy petting that might have been a feature had the film gone straight-to-video forty years ago. Instead, Blackhurst and McGuire pursue the dullest and most careworn of horror-movie plots, the investigation into the events of a prologue, undamming waves of exposition that don't make a huge amount of sense, all told. (The problem's "magic water", apparently.) A solid enough advert for the efficacy of today's waterproofed film cameras - but it makes for a rather soggy kebab, I'm afraid.

Night Swim is now showing in selected cinemas.