Romantic comedy is generally structured tighter than an atom: Mess with its neutrons, protons and electrons at your peril. In "Prime," you can tell filmmaker Ben Younger understands the physics but isn't afraid to smash that atom.

Sure, this romance, starring Meryl Streep, Uma Thurman and Bryan Greenberg, follows a familiar boy-meets-girl scenario, but Younger turns the routine into combustible fun. That's why, for instance, the two lovers in our story are the thirty-something Rafi (Thurman), who can hear the baby clock ticking, and the 23-year-old David (Greenberg), whose idea of a good time is playing Nintendo.

It's also why -- in the movie's central complication -- Rafi talks openly about her romantic issues with a therapist, Lisa (Streep), who happens to be David's very devout Jewish mom and would disapprove of this union with an older shiksa. Neither woman makes the David connection for a while, and that's uncomfortably amusing enough. But when Lisa finds out and insists on continuing the sessions (while Rafi remains in the dark), the movie really becomes "Prime." Streep is meant to be the third party here, but she rapidly becomes the drama's most entertaining nucleus. Her stunned reactions as she listens to Rafi's increasingly colorful anecdotes are one of many reasons to watch this.

-- Desson Thomson

Rafi (Uma Thurman, right) dates her therapist's (Meryl Streep) son in "Prime."