Much is going to be made of the circumstances surrounding Threshold, the micro-budget supernatural road movie by co-directors Powell Robinson and Robert-Patrick Young, which arrives via always-immaculate horror specialists Arrow this week. Shot on two iPhones over two days, with a crew of three and dialogue mostly improvised by its two leads, there’s no doubt that it’s an impressive example of turning limitations into virtues (this writer didn’t even know about the iPhones until after I’d seen it, and never I never felt it was particularly cheap or low-tech when it was on screen). The against-the-odds achievement of getting a film made under those conditions, as impressive as that is,is really the least important thing here, though. iPhones are just handy-sized cameras, after-all, and the wide vistas of an American cross-country trip ensure the frame is almost always cinematic and often quite beautiful.

This isn’t a story about budget filmmaking, it’s a story about connections. We follow Leo (Joey Millin) as he drags the semi-trashed car he used as a teenager out of mothballs to meet up with his estranged sister, Virginia (Madison West), who has suddenly resurfaced after losing touch with her family. It turns out that Virginia, struggling with addiction, has joined a cult, which helped her get clean but also performed a strange ritual that has left her ‘bonded’ to a strange man, each feeling what the other feels. Reconnecting with her brother, she talks him into driving her across the country to find her opposite number in the hope they can lift the curse.

ThresholdThe conceit is clever and relatively well explored ­– at one particularly creepy point Virginia has an orgasm out nowhere; later she will scratch ‘where are you?’ into her arm in an attempt to communicate with her unknown partner­­­ – the supernatural bond isn’t the most important one in the film, however. At its heart Threshold is an odd-couple road movie, and it’s the relationship between the two siblings that makes the film work. Millin and West have solid chemistry and have clearly worked hard on their connection and back story; the two improvise with an impressive, naturalistic fluidity, nailing both the unresolved resentments of estrangement and the natural groove that a brother and sister will ultimately always fall into. Their bickering, both serious and silly, is 99% of why the film works.

Robinson and Young explore connection in other ways too. The car, complete with a CD of his old punk band still in the stereo, connects Leo to the pair’s past, while his phone connects him to his wife, whom he is in the process of separating from, and his daughter, who has never known her aunt. Meanwhile Leo connects Virginia to her former life, and his daughter Ally is her bridge to a possible future as a member of the family. These lines are all drawn subtly, nodded at through Millin and West’s endearingly natural improvisation.

As a horror movie, Threshold more-or-less holds its own, though it’s more effective as a drama than it is as an exercise in suspense. There are a few good scares along the way, especially during a pause in the pair’s journey in which they rent what looks suspiciously like the house from Netflix’s Malcolm & Marie, spoiled by the arrival of an unexpected guest from down the road.

Ultimately, though, the film is more comfortable as a quirky road drama than it is a scary movie, working best when it’s nodding to Gregg Araki’s cult classic The Doom Generation than, say, Jeepers Creepers. It’s highlighted by a slightly rushed ending that doesn’t quite live up the film’s premise and is the only time that the low budget and basic staging leaks onto the screen. Ultimately, though, this is more about the journey than the destination, and on that level it’s an admirable achievement.