Some movies pack so many plots, subplots and characters into their running time that you just about need a chart to keep them all straight. Night Moves is not one of those movies.

It sticks to three basic characters and a slim plot that could be summarized in little more than a minute. None of this will surprise fans of director/co-writer Kelly Reichardt (Meek’s Cutoff), who favors subtle character study over action, but other viewers should be prepared to exercise a little patience.

This is the kind of film we used to describe as “glacial” before the glaciers started melting and retreating due to global warming—which, by the way, is something the three protagonists presumably know something about. They’re all radical environmentalists, and they’ve come together to blow up a hydroelectric dam in the Pacific Northwest.

Josh (Jesse Eisenberg) and Dena (Dakota Fanning) appear to be casual friends who live in the same community. Harmon (Peter Sarsgaard) is a former soldier who has laid the groundwork for the attack by purchasing the fertilizer needed to produce the explosion.

Or most of the fertilizer: The first complication is that he doesn’t have enough, sending Dena to the local farm-supply store in hopes of purchasing more despite rules designed to prevent just the kind of terrorist act they’re planning.

Beyond that glitch, things go remarkably smoothly as the bombers-to-be buy a used boat—named Night Moves, thus giving the flick its title—and otherwise make the final preparations. It’s only after they launch their attack on the dam that they learn something has gone very wrong.

Night Moves is most interesting during the first half, when the three treat each other with the kind of tense suspicion that grows naturally out of planning an illegal act with people you barely know. All three actors do a good job of delineating their characters despite minimal help from the script.

Still, it would be nice if we knew more about the trio. For starters, we’re told little about their reasons for blowing up the dam, except that it’s bad for the fish and exists solely to satisfy people’s demand for electronic gadgetry. The focus is on the “how” of their attack rather than the “why.”

The post-attack portion of the film is even less detailed. It’s basically a portrait of rising regret and paranoia, and it’s drawn almost entirely on Josh’s glum face, as Harmon and Dena have retreated into the background. Eisenberg is an interesting actor in the right role, but he can’t do much with what little the script gives him to work with.

By the end, it appears the only question Reichardt seeks to answer is whether people who’ve done something stupid and desperate will follow it up by doing something even more stupid and desperate. If she made the answer a little less obvious, Night Moves would be a better film.

Rating: 2½ stars (out of 5)

Little sis goes looking for star-struck big sis

This seems to be the week for small films that begin stronger than they end.

Elena, an autobiographical documentary directed by Petra Costa, starts by enveloping us in a collage of narration and impressionistic images. We’re told that Petra, a young Brazilian, has set off for New York in hopes of finding her older sister, Elena Andrade.

Home-movie footage and tape recordings help to fill in a portrait of Elena, a beautiful woman who was drawn to the performing arts—as her mother had been before giving it all up to start a family. Elena achieved some success acting and dancing in avant-garde theater in Sao Paulo, but it wasn’t enough for her. So, years ago, she left to seek movie stardom in the Big Apple.

Then, after sending home occasional tape recordings detailing her attempts to become noticed, Elena abruptly dropped out of sight. What happened to her?

To the extent that the film addresses that question, it’s compelling. Eventually, though, we learn that Petra already knows full well what happened to her big sister. From this point on, the film’s focus switches to Petra herself and the question of whether she’ll follow in Elena’s unhappy footsteps.

This appears to be a real possibility, as Petra has inherited her sister’s interest in the cinema. Indeed, Elena seemed to be grooming her for such a future when they were growing up, giving the little girl starring roles in their home movies.

Still, the switch in focus from Elena to Petra makes the film seem more like a personal journal than a work of art. The beautiful, impressionistic images continue, but they begin to seem self-serving and even self-indulgent.

Though it begins promisingly, and though it runs only 80 minutes, Elena finally overstays its welcome.

Rating: 3 stars (out of 5)

Night Moves (rated R) and Elena (unrated) open Friday (June 13) at the Gateway Film Center.