Though it moves at her characteristically deliberate pace, Kelly Reichardt’s eco-thriller delivers considerable tension in telling what’s actually quite a simple story. Essentially “Night Moves” shows, in sometimes excruciating detail, an act of domestic terrorism and the effect it has on two of its perpetrators. And in doing so it manages to elicit a degree of understanding, if not sympathy, for characters whose obsessive beliefs blind them to the potential ramifications of their actions.

The film begins with Josh (Jesse Eisenberg) and Dena (Dakota Fanning) purchasing a used boat. But it’s not for their amusement They’re a pair of Oregon environmentalists—he lives at an agricultural commune, and she works at what appears to be a New Age homeopathic spa—and intend to use the vessel to destroy on hydroelectric dam as a message that such intervention in the natural order of things will no longer be tolerated. Taking their purchase to the remote site where Harmon (Peter Sarsgaard), an ex-Marine with explosives skill, lives in a run-down trailer, they plan to load it with the ammonium nitrate he’s collected over time and quietly take it to the dam by night, using a timer to detonate it after they make their escape.

Much of the suspense that Reichardt generates in connection with the plot lies in the way she dwells on the mechanics. Even the purchase of the boat, in which Dana is exuberant and upbeat while Josh looks on sullenly, has a tense undercurrent, and when the pair arrive at Harmon’s trailer to find that he hasn’t collected quite enough fertilizer to suit their needs, it leads to an effective sequence in which Dana tries to persuade the owner (James Le Gros) of an agricultural-products emporium to sell her five hundred pounds of the stuff without the required post-9/11 identification. The prolonged episode in which the plotters drive to the park where they’ll launch the boat, quietly row it to the dam, and set the explosives to detonate is also cleverly handled, with an unexpected intervention by a passerby that proves a model of the distinction Hitchcock drew between shock and suspense.

The explosion itself isn’t the occasion for big Hollywood special pyrotechnics—for one thing this is a low-budget affair, but the blast isn’t Reichardt’s main point of interest anyway. Her focus instead is on the aftermath of the act, which has several unexpected casualties. Though the way Josh and Dana react to the consequences of what they’ve done doesn’t carry the same level of tension as the earlier part of the film (and some might find what happens between them a mite implausible), this latter section of the picture does bring home the point that however idealistic such activism might seem, it can destroy far more than what it aims at.

The success of the film is greatly dependent on mood, and Reichardt benefits from Christopher Blauvelt’s atmospheric camerawork as well as her own editing, which gives scenes the time to unfold with the deliberation she wants, even if to some the pacing will seem unnecessarily languid. (One man’s hypnotic will be another’s interminable.) And the cast respond with committed performances. Eisenberg dominates with a portrait of a grimly determined fellow whose pose fractures under pressure, but Fanning partners him well as a person whose high principles are sorely tested when things take a negative turn. Sarsgaard remains the most opaque of the trio, but he brings a gruff matter-of-factness to the more experienced Harmon, while Le Gros is nicely natural as the reluctant salesman.

Like Reichardt’s earlier films, “Night Moves” takes patience to appreciate. But if you’re willing to succumb to its admittedly glacial pacing, you may well find yourself drawn into an unfamiliar world that, in her hands, is worth visiting.