Kelly Reichardt makes films about people who are in lost in their environment.

Old Joy was about two friends lost in the woods, Wendy And Lucy about a woman who's lost her dog in a strange town, Meek's Cutoff about Old West settlers lost on the trail. Her new film is an intriguing variation on the theme - this time her main character is at one with his environment, with nature, indeed fights to protect it; but he's lost within himself.

It's interesting to see how a director, whose stock in trade is a miniaturist's single-minded focus on human nature and minimal scenarios, moves into a more genre-based mainstream. Just as Meek's Cutoff was a revisionist foray into the western, so Night Moves tiptoes into thriller territory without sacrificing any of Reichardt's meticulous, slow-paced delineation of character and place.

As ever with her, the action is set in Oregon, where we're introduced to a band of radical environmentalists willing to take violent action in order to make their point. While sharing a common purpose, they couldn't be more different. Their leader, Josh (Jesse Eisenberg), works on an organic farm and his environmental concerns are the most innate; at the same time he's insular, taciturn, humourless. Dena (Dakota Fanning) is a canny rich kid who's rebelled, now works in a Zen spa and whose politicisation is learned, well-researched; Harmon (Peter Sarsgaard) is a former marine, disillusioned and apparently more concerned with the anarchic deed than the reasons behind it.

Together they meticulously plan to blow up a hydroelectric dam, which they regard as symptomatic of resource-hungry modern society. Josh lends the impetus, Harmon the know-how and Dena the cash - it's she who buys the eponymous speedboat that will ferry them and their incendiary cargo to the foot of the dam.

Yet the girl is no slouch. One of the film's most enjoyable scenes involves her attempt to purchase an attention-raising amount of fertilizer, fuel of their bomb, with the self-possession of a seasoned con artist. It typifies Reichardt's opening half, which follows preparation and terrorist act with the detail and deliberate pacing of a police procedural. The attack on the dam is brilliantly orchestrated, the tension cranking up in the silence of night, the risk of getting caught allied to the very real possibility of the group blowing themselves up.

I won't say how that pans out. But, in the aftermath, the film takes a surprising route, one in which Reichardt and her regular co-writer Jonathan Raymond dig deeper into the psychology of political activism, reminding us that a political conscience isn't necessarily accompanied by a moral one.

Living in a pastoral idyll, on the organic farm, hasn't made Josh a pleasant or rounded person. Here is a man who will protect a bird's nest, and wants to save the world, but is at no pains to connect with people. Nor does he understand them. When anticipating the effect of the bomb he declares that "People are going to start thinking. They have to." It is startlingly naïve.

Eisenberg is a dab hand at playing people uncomfortable amongst others, not least Mark Zuckerberg in The Social Network. Until now the underlying characteristic has been haughty arrogance; here the actor presents a goateed and glum isolation that is increasingly chilling.

The aftermath of the attempt on the dam is less interesting than the build-up; it feels more conventional. That said, with Reichardt's less-is-more mode, the film continues to be an intense and fascinating alternative to Hollywood's innumerable bonehead thrillers.