Julia Garner. left, and Lily Tomlin in Grandma (Glen Wilson/Sony Pictures Classics}

Isn’t that sweet old Lily Tomlin starring as a senior citizen in Grandma? Damn right, and Grandma will cut a bitch. Tomlin masterfully plays Elle Reid, a broke, has-been poet and washed-up academic who stages lethal ambushes of the unwary with corrosive cynicism and anger. When we first see Elle, she’s heartlessly dumping her stunned younger girlfriend (Judy Greer). And when her naïve teenaged granddaughter, Sage (Julia Garner), unexpectedly shows up in trouble—yes, that kind of trouble—Elle’s got some acrid words for her, too. Forget a bull in a china shop, Elle Reid is a breakdancing hippopotamus who smashes crockery everywhere she goes.

But Elle is also loyal, smart, and a bit of a gambler. After a tense exchange, Elle and Sage are going to pile into Elle’s wheezy old Dodge, tooling across Los Angeles to drum up some cash to straighten out Sage’s little problem before the 5:45 appointment that afternoon. Friends and foes will reveal themselves. Sorrows will be reckoned with, secrets will be uncovered, and viewers’ hearts will be broken and warmed by Paul Weitz’s funny, smart, loveable film.

At first sitcomish, Grandma gathers unexpected power and depth as the two women roll down the highway. Elle is grieving over a loss of her own, and now her granddaughter’s predicament has finally handed her a cause worth fighting for. Tomlin delivers acid putdowns with spot-on timing and gets her ya-yas out cold-cocking a snotty teenage boy with a hockey stick. Her performance crackles with the rush of a character (and actress) breaking free to wield mighty powers, and it energizes what could have been a wistful indie chamber piece with a thrilling sense of catharsis and release.

How does a teenager cope with such a formidable force? Flummoxed by Grandma’s antics and spooked by the ticking clock, wet-behind-the-ears Sage can’t face conflict or stick up for herself. Well, Elle’s got some news for Little Miss Thing: in this life you’ve got to kick some ass or die. Sage will learn to appreciate Elle’s nerve. Julia Garner is endearing as a sweet, unformed young woman suddenly exposed to a gauntlet of odd characters and raw feelings.

The two actresses have a lovely rapport, and Grandma’s script cleverly plays up the generation gap between the old-school feminist and clueless Millennial. When was the last time you heard Simone de Beauvoir and Germaine Greer name-dropped in a movie? After a chance meeting ends with Elle and her ex screaming “Solipsist!” and “Ingénue!” at each other, Sage chimes in: “Well, at least I’m learning some new insults.”

Grandma contains many comical and affecting set pieces, but two emotional high points pack a particular punch. In one, Elle tries to hit up a rich old flame (Sam Elliott) for some dough. The exposer of others’ foibles gets a run for her money as Elliott’s crafty old fox holds up a mirror to her own self-deception. Their subtle, beautifully played face-off goes from an edgy contest of wits to a requiem for a sad, lost past.

Another standout scene plays out the confrontation with Sage’s mother, a corporate Superwoman who Elle and Sage derisively refer to as “Judge Judy.” Marcia Gay Harden turns in a moving performance as a crass, hard-charging powerhouse who is also a human being and whose frustration and disappointment at her daughter’s screwup are completely relatable. With setbacks and false starts, Judy, too, will soften up and learn something about herself and the people she loves.

Unafraid to raise difficult emotions, bristling with humor, conflict, and truth, Grandma ends on a note of hard-won peace. The film’s touch is light, but its satisfactions deep. It is principled in its understated but firm pro-choice stance, welcome in its message of forgiveness, and overdue in its faith that the young and the old have so much to offer each other if they would only take a little time to care and to listen. Don’t let this wonderful movie pass you by.