After the intriguing Primer, hopes were high for Shane Carruth's new movie – but it has turned out to be a baffling, opaque mess. But at least it's got a baby pig

It took me three viewings to understand Primer, Shane Carruth's 2004 Sundance grand jury prize-winner. And I liked it. So by the time Monday afternoon rolled around in Park City I was a drop in an ocean of well-wishers who flooded into the Eccles theatre to see the world premiere of Carruth's long-awaited follow-up, Upstream Color.

In his introductory comments, festival director John Cooper urged us to pay close attention to what we were about to see and promised we would have plenty of questions. Ninety-six minutes later I'd venture to suggest there was only one question that everybody wanted to ask. Yet when an audience member summoned the courage to ask Carruth what the movie was about he sounded mildly exasperated.

"Ah, so the plot didn't land," he said, provoking scattered laughter, although to be honest most of us sank a little deeper into our seats. Carruth, a former engineer, then stumbled through a long-winded attempt to explain part of his movie, although he might have been a little crestfallen.

Upstream Color contains striking microscopic imagery, cute pigs and alarmingly aggressive foley work. It's meticulous, methodical and educated – but also extreme, and extremely pretentious. I realise this is an eccentric suite of compliments, but here's the plot, such as it is. It's not going to spoil the movie.

A man, who may be the Thief, scrapes a leaf in his greenhouse and frowns. He kidnaps a woman and forces her to ingest a worm. He hypnotises her and embezzles money from her. He makes her read from Walden, the self-reliance manual by the 19th century transcendentalist Henry David Thoreau.

The woman is transferred to a pig corral where a peculiar fellow with a fondness for white noise performs surgery and transfers something from the body of a baby pig into her body. She regains consciousness in a stationary car on the side of a freeway. She returns home and excises a worm or three from beneath her skin. She loses her job.

She meets a sympathetic former broker, played by Carruth. They fall in love. They learn of others who ingested worms. Maybe the man did, too. They send each person a copy of Walden. Orchid harvesters by a river discover blue orchids, which were once white. The peculiar pig fellow turns up here and there, but nobody appears to see him. He throws a pig in a bag off a bridge. Later, blue powder escapes into a river. Or maybe this happened earlier. Time is elastic. Carruth would agree.

The man and the woman track down the peculiar pig-throwing fellow at the pig corral. The woman shoots him. They call in vets to give the pigs a check-up. Other former worm ingesters arrive and paint the corral a happy yellow. Somewhere, the man who may be the Thief looks worried. The woman cuddles a smiling baby pig.

We the audience leave in silence. Theories are proposed and discussed. Is it a love story with an activism thriller on the side? Or perhaps the quest for universal theory? This might be a brilliant movie way ahead of its time – the kind of avant-garde piece you'd expect to see in the festival's New Frontiers programme. But the powers that be positioned it in the US Dramatic Competition so it would be seen and become a talking point. That was its biggest success of the day.