The best thing about "Groove" is its soundtrack. A constant, underlying presence throughout the film, the music serves as a kind of heartbeat, so much so that when it stops for just a moment--when a character who's on ecstasy for the first time wakes up from his drug-and-love-induced stupor--its absence is strikingly noticeable.

   That's not to undersell the film, a night-in-the-life of San Francisco ravers. Colin Turner (Denny Kirkwood), planning to propose to his girlfriend Harmony (Mackenzie Firgens), invites his older brother David (Hamish Linklater) to join them at an underground party. David, a writer making ends meet by composing computer manuals, is skeptical but agrees to attend for his brother's big surprise. What he finds, however, is love for himself.

   But the plot really serves as an excuse to film an atmosphere where the pumping, thumping music inspires everybody to dance, DJs are viewed as gods, and the host puts on the unfinanced event simply for the post-party nod of recognition. Though loud and raucous on the surface, the rave is relatively safe (no alcohol is served, just water and hippy-dippy X) and benign enough that even a neighborhood cop, after a tour of the abandoned building-cum-faux-new-computer-company, tells the party planners to simply keep their ravers inside; the only violence here is in the body-shaking groovin' goin' on. Starring Lola Glaudini, Hamish Linklater, Denny Kirkwood and Mackenzie Firgens. Directed and written by Greg Harrison. Produced by Greg Harrison and Danielle Renfrew. A Sony Pictures Classics release. Drama. Rated R for drug use, language and brief sexuality. Running time: 86 min