In “BPM,” Arnaud Valois, center, plays Nathan, a new member of the AIDS activist group ACT UP who is initially mistrusted because he is HIV-negative. (Celine Nieszawer/The Orchard)

The fast-paced opening of the French drama "BPM (Beats Per Minute)" captures the thrill of being young, committed and supremely incensed: Activists from the Paris branch of the AIDS advocacy group ACT UP storm a government AIDS conference, hurling balloons full of what appears to be blood, even handcuffing one of the speakers.

Filmmaker Robin Campillo depicts this brazen assault along with the subsequent second-guessing, intercutting between flashbacks and flash-forwards that include the group's next weekly meeting, where the messy action is both defended and critiqued. ACT UP-Paris was an offshoot of the group founded in New York in 1987 as a response to inaction on the AIDS crisis, but its insistence on rigorous dialectic appears very French.

This portrayal is probably accurate, because Campillo and co-writer Philippe Mangeot were there: Both were members of the French chapter of ACT UP (AIDS Coalition to Unleash Power) in the early 1990s, when this film is set. Yet "BPM" is not a docudrama, even though cinematographer Jeanne Lapoirie's handheld camera prowls through the proceedings as if shooting pure cinéma vérité.

Campillo's style is usually naturalistic, and the superb ensemble cast's performances are entirely unaffected. At first, meeting coordinators Sophie (Adèle Haenel) and Thibault (Antoine Reinartz) stand out. But "BPM," like ACT UP, is a democracy. So we get to know many others, including Hélène (Catherine Vinatier) and her teenage hemophiliac son, Marco (Théophile Ray), the group's brewer of fake blood.

Adèle Haenel stars as Sophie in “BPM.” (Celine Nieszawer/The Orchard)

Later, the focus shifts to Nathan (Arnaud Valois), a new member who's initially mistrusted for being HIV-negative, and his developing romance with Sean (Nahuel Pérez Biscayart). Sean is one of the group's most militant members — not to mention one of its most sickly.

The principal plotlines are linked by more lyrical moments, including microscopic views of cells, an ominous vision of the Seine and slow-motion revelries at dance clubs. The music rarely revs to 120 BPM, the cadence specified in the film's original French title, and only two songs supplement Arnaud Rebotini's electronic — but seldom banging — score.

"BPM" is often exhilarating and ultimately moving, but it makes few concessions to audiences without a strong preexisting interest in its subject. At nearly 2 ½ hours, the film would benefit from a tighter edit. The jumpy, intriguingly cursory scenes of the first hour later yield to sequences that linger a few beats (or more) too long.

What's more, Campillo provides little historical background and doesn't offer any quick medical tutorials. Some viewers will understand the frustrating state of HIV-AIDS science 25 years ago, but many won't. One of the movie's themes — the distribution of tainted blood for transfusions — is a specifically French scandal that goes unexplained.

Yet anyone who has ever attended a contentious meeting will understand one crucial aspect of the movie's dynamic. Although the life-or-death nature of ACT UP's campaign gives it a special urgency, organizing for a common cause never goes as smoothly as it seems it should. As one of the film's allies/antagonists explains to another, in a quiet moment, "We don't like each other, but we're friends."

Unrated. At Landmark's E Street Cinema. Contains explicit sex, nudity and obscenity. In French with subtitles. 142 minutes.